docs: Major cleanup - 46 → 12 essential docs

MASSIVE DOCUMENTATION CLEANUP:
- Reduced from 46 docs to 12 essential files
- Archived 34 outdated planning and analysis documents

✅ KEPT (Essential for current operations):
- STUDENT_QUICKSTART.md - Student onboarding
- INSTRUCTOR_GUIDE.md - Instructor setup
- cifar10-training-guide.md - North star achievement
- tinytorch-assumptions.md - Complexity framework (NEW)
- tinytorch-textbook-alignment.md - Academic alignment

- NBGrader integration docs (3 files)
- Development standards (3 files)
- docs/README.md - Navigation guide (NEW)

🗑️ ARCHIVED (Completed/outdated planning):
- All optimization-modules-* planning docs
- All milestone-* system docs
- All tutorial-master-plan and analysis docs
- Module reordering and structure analysis
- Agent setup and workflow case studies

RESULT: Clean, focused documentation structure
Only active, current docs remain - easy to find what you need!

docs/README.md

@@ -0,0 +1,35 @@
+# TinyTorch Documentation
+
+This directory contains essential documentation for TinyTorch development and usage.
+
+## 📚 User Documentation
+
+- **`STUDENT_QUICKSTART.md`** - Getting started guide for students
+- **`INSTRUCTOR_GUIDE.md`** - Setup and grading guide for instructors
+- **`cifar10-training-guide.md`** - Complete guide to achieving the north star goal (75% CIFAR-10 accuracy)
+
+## 🔧 Development Documentation
+
+- **`tinytorch-assumptions.md`** - **CRITICAL**: TinyTorch complexity framework and implementation guidelines
+- **`tinytorch-textbook-alignment.md`** - Alignment with ML systems textbooks
+
+### Development Standards
+- **`development/module-rules.md`** - Module development standards and patterns
+- **`development/nbgrader-standardized-testing.md`** - Testing standards
+- **`development/nbgrader-testing-template.md`** - Testing templates
+
+### NBGrader Integration
+- **`nbgrader/NBGrader_Quick_Reference.md`** - Daily use commands and workflow
+- **`nbgrader/NBGRADER_STYLE_GUIDE.md`** - Style guide for NBGrader cells
+- **`nbgrader/NBGrader_Text_Response_Technical_Implementation.md`** - Technical implementation details
+
+## 📦 Archive
+
+The `archive/` directory contains historical documentation that's no longer actively maintained but preserved for reference.
+
+---
+
+**Start here**:
+- **Students**: Read `STUDENT_QUICKSTART.md`
+- **Instructors**: Read `INSTRUCTOR_GUIDE.md`
+- **Developers**: Read `tinytorch-assumptions.md` FIRST, then `development/module-rules.md`