build: add PDF generation infrastructure for book

Add build scripts and GitHub Actions workflow to support PDF generation:
- build_pdf.sh: LaTeX-based PDF build for professional quality
- build_pdf_simple.sh: HTML-to-PDF build without LaTeX requirement
- Makefile: convenient shortcuts for common build tasks
- GitHub Actions workflow: automated PDF builds on demand

Supports multiple output formats:
- HTML website (default, via jupyter-book)
- PDF via HTML-to-PDF (pyppeteer, no LaTeX needed)
- PDF via LaTeX (professional typography, requires LaTeX)

Usage:
  make html        - Build HTML website
  make pdf-simple  - Build PDF without LaTeX
  make pdf         - Build PDF with LaTeX

.github/workflows/build-pdf.yml

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+name: Build TinyTorch PDF
+
+# Build PDF version of the book
+# Runs manually or on release tags
+on:
+  workflow_dispatch:
+    inputs:
+      method:
+        description: 'Build method (simple or latex)'
+        required: true
+        default: 'simple'
+        type: choice
+        options:
+          - simple
+          - latex
+  release:
+    types: [published]
+
+jobs:
+  build-pdf:
+    runs-on: ubuntu-latest
+    
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v4
+
+    - name: Set up Python
+      uses: actions/setup-python@v4
+      with:
+        python-version: '3.11'
+        cache: 'pip'
+
+    - name: Install base dependencies
+      run: |
+        pip install --upgrade pip
+        pip install "jupyter-book<1.0"
+        pip install -r book/requirements.txt
+
+    - name: Install LaTeX (if latex method)
+      if: github.event.inputs.method == 'latex' || github.event_name == 'release'
+      run: |
+        sudo apt-get update
+        sudo apt-get install -y \
+          texlive-latex-extra \
+          texlive-fonts-recommended \
+          texlive-latex-recommended \
+          latexmk
+
+    - name: Install pyppeteer (if simple method)
+      if: github.event.inputs.method == 'simple' || github.event.inputs.method == ''
+      run: |
+        pip install pyppeteer
+        # Pre-download Chromium to avoid timeout during build
+        python -c "from pyppeteer import chromium_downloader; chromium_downloader.download_chromium()"
+
+    - name: Build PDF (simple method)
+      if: github.event.inputs.method == 'simple' || github.event.inputs.method == ''
+      run: |
+        cd book
+        jupyter-book clean . --all
+        jupyter-book build . --builder pdfhtml
+        # Copy to standard location
+        mkdir -p _build/pdf-output
+        cp _build/pdf/book.pdf _build/pdf-output/tinytorch-course.pdf
+
+    - name: Build PDF (LaTeX method)
+      if: github.event.inputs.method == 'latex' || github.event_name == 'release'
+      run: |
+        cd book
+        jupyter-book clean . --all
+        jupyter-book build . --builder pdflatex
+        # Copy to standard location
+        mkdir -p _build/pdf-output
+        cp _build/latex/tinytorch-course.pdf _build/pdf-output/tinytorch-course.pdf
+
+    - name: Upload PDF artifact
+      uses: actions/upload-artifact@v4
+      with:
+        name: tinytorch-pdf-${{ github.event.inputs.method || 'latex' }}-${{ github.sha }}
+        path: book/_build/pdf-output/tinytorch-course.pdf
+        retention-days: 90
+
+    - name: Upload to release (if release event)
+      if: github.event_name == 'release'
+      uses: softprops/action-gh-release@v1
+      with:
+        files: book/_build/pdf-output/tinytorch-course.pdf
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+    - name: Build summary
+      run: |
+        echo "## 📚 PDF Build Complete" >> $GITHUB_STEP_SUMMARY
+        echo "" >> $GITHUB_STEP_SUMMARY
+        echo "**Method:** ${{ github.event.inputs.method || 'latex' }}" >> $GITHUB_STEP_SUMMARY
+        echo "**File:** tinytorch-course.pdf" >> $GITHUB_STEP_SUMMARY
+        echo "**Size:** $(du -h book/_build/pdf-output/tinytorch-course.pdf | cut -f1)" >> $GITHUB_STEP_SUMMARY
+        echo "" >> $GITHUB_STEP_SUMMARY
+        echo "Download the PDF from the artifacts section above." >> $GITHUB_STEP_SUMMARY
+

book/Makefile

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+# TinyTorch Book Build Makefile
+# Convenient shortcuts for building HTML and PDF versions
+
+.PHONY: help html pdf pdf-simple clean install test
+
+help:
+	@echo "TinyTorch Book Build Commands"
+	@echo "=============================="
+	@echo ""
+	@echo "  make html        - Build HTML version (default website)"
+	@echo "  make pdf         - Build PDF via LaTeX (requires LaTeX installation)"
+	@echo "  make pdf-simple  - Build PDF via HTML (no LaTeX required)"
+	@echo "  make clean       - Remove all build artifacts"
+	@echo "  make install     - Install Python dependencies"
+	@echo "  make install-pdf - Install dependencies for PDF building"
+	@echo "  make test        - Test build configuration"
+	@echo ""
+	@echo "Quick start for PDF:"
+	@echo "  make install-pdf && make pdf-simple"
+	@echo ""
+
+html:
+	@echo "🌐 Building HTML version..."
+	jupyter-book build .
+
+pdf:
+	@echo "📚 Building PDF via LaTeX..."
+	@./build_pdf.sh
+
+pdf-simple:
+	@echo "📚 Building PDF via HTML..."
+	@./build_pdf_simple.sh
+
+clean:
+	@echo "🧹 Cleaning build artifacts..."
+	jupyter-book clean . --all
+	rm -rf _build/
+
+install:
+	@echo "📦 Installing base dependencies..."
+	pip install -U pip
+	pip install "jupyter-book<1.0"
+	pip install -r requirements.txt
+
+install-pdf:
+	@echo "📦 Installing PDF dependencies..."
+	pip install -U pip
+	pip install "jupyter-book<1.0" pyppeteer
+	pip install -r requirements.txt
+
+test:
+	@echo "🧪 Testing build configuration..."
+	jupyter-book config sphinx .
+	@echo "✅ Configuration valid"
+
+# Default target
+.DEFAULT_GOAL := help
+

book/build_pdf.sh

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+#!/bin/bash
+# Build PDF version of TinyTorch book
+# This script builds the LaTeX/PDF version using jupyter-book
+
+set -e  # Exit on error
+
+echo "🔥 Building TinyTorch PDF..."
+echo ""
+
+# Check if we're in the book directory
+if [ ! -f "_config.yml" ]; then
+    echo "❌ Error: Must run from book/ directory"
+    echo "Usage: cd book && ./build_pdf.sh"
+    exit 1
+fi
+
+# Check dependencies
+echo "📋 Checking dependencies..."
+if ! command -v jupyter-book &> /dev/null; then
+    echo "❌ Error: jupyter-book not installed"
+    echo "Install with: pip install jupyter-book"
+    exit 1
+fi
+
+if ! command -v pdflatex &> /dev/null; then
+    echo "⚠️  Warning: pdflatex not found"
+    echo "PDF build requires LaTeX installation:"
+    echo "  - macOS: brew install --cask mactex-no-gui"
+    echo "  - Ubuntu: sudo apt-get install texlive-latex-extra texlive-fonts-recommended"
+    echo "  - Windows: Install MiKTeX from miktex.org"
+    echo ""
+    echo "Alternatively, use HTML-to-PDF build (doesn't require LaTeX):"
+    echo "  jupyter-book build . --builder pdfhtml"
+    exit 1
+fi
+
+echo "✅ Dependencies OK"
+echo ""
+
+# Clean previous builds
+echo "🧹 Cleaning previous builds..."
+jupyter-book clean . --all || true
+echo ""
+
+# Build PDF via LaTeX
+echo "📚 Building LaTeX/PDF (this may take a few minutes)..."
+jupyter-book build . --builder pdflatex
+
+# Check if build succeeded
+if [ -f "_build/latex/tinytorch-course.pdf" ]; then
+    PDF_SIZE=$(du -h "_build/latex/tinytorch-course.pdf" | cut -f1)
+    echo ""
+    echo "✅ PDF build complete!"
+    echo "📄 Output: book/_build/latex/tinytorch-course.pdf"
+    echo "📊 Size: ${PDF_SIZE}"
+    echo ""
+    echo "To view the PDF:"
+    echo "  open _build/latex/tinytorch-course.pdf    # macOS"
+    echo "  xdg-open _build/latex/tinytorch-course.pdf  # Linux"
+    echo "  start _build/latex/tinytorch-course.pdf     # Windows"
+else
+    echo ""
+    echo "❌ PDF build failed - check errors above"
+    echo ""
+    echo "📝 Build artifacts in: _build/latex/"
+    echo "Check _build/latex/tinytorch-course.log for detailed errors"
+    exit 1
+fi
+

book/build_pdf_simple.sh

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+#!/bin/bash
+# Build PDF version of TinyTorch book (Simple HTML-to-PDF method)
+# This script builds PDF via HTML conversion - no LaTeX installation required
+
+set -e  # Exit on error
+
+echo "🔥 Building TinyTorch PDF (Simple Method - No LaTeX Required)..."
+echo ""
+
+# Check if we're in the book directory
+if [ ! -f "_config.yml" ]; then
+    echo "❌ Error: Must run from book/ directory"
+    echo "Usage: cd book && ./build_pdf_simple.sh"
+    exit 1
+fi
+
+# Check dependencies
+echo "📋 Checking dependencies..."
+if ! command -v jupyter-book &> /dev/null; then
+    echo "❌ Error: jupyter-book not installed"
+    echo "Install with: pip install jupyter-book pyppeteer"
+    exit 1
+fi
+
+# Check if pyppeteer is installed
+python3 -c "import pyppeteer" 2>/dev/null || {
+    echo "❌ Error: pyppeteer not installed"
+    echo "Install with: pip install pyppeteer"
+    echo ""
+    echo "Note: First run will download Chromium (~170MB)"
+    exit 1
+}
+
+echo "✅ Dependencies OK"
+echo ""
+
+# Clean previous builds
+echo "🧹 Cleaning previous builds..."
+jupyter-book clean . --all || true
+echo ""
+
+# Build PDF via HTML
+echo "📚 Building PDF from HTML (this may take a few minutes)..."
+echo "ℹ️  First run will download Chromium browser (~170MB)"
+jupyter-book build . --builder pdfhtml
+
+# Check if build succeeded
+if [ -f "_build/pdf/book.pdf" ]; then
+    # Copy to standard location with better name
+    cp "_build/pdf/book.pdf" "_build/tinytorch-course.pdf"
+    PDF_SIZE=$(du -h "_build/tinytorch-course.pdf" | cut -f1)
+    echo ""
+    echo "✅ PDF build complete!"
+    echo "📄 Output: book/_build/tinytorch-course.pdf"
+    echo "📊 Size: ${PDF_SIZE}"
+    echo ""
+    echo "To view the PDF:"
+    echo "  open _build/tinytorch-course.pdf           # macOS"
+    echo "  xdg-open _build/tinytorch-course.pdf       # Linux"
+    echo "  start _build/tinytorch-course.pdf          # Windows"
+else
+    echo ""
+    echo "❌ PDF build failed - check errors above"
+    exit 1
+fi
+