Simplify book directory structure

✅ Remove unnecessary nesting: book/tinytorch-course/ → book/
✅ Update all path references in scripts and workflows
✅ Cleaner development experience with shorter paths
✅ Book builds successfully with simplified structure

Changes:
- Move all book files up one directory level
- Update convert_modules.py paths
- Update GitHub Actions workflow paths
- Update book configuration paths
- Test confirms everything works correctly

.github/workflows/deploy-book.yml

@@ -45,7 +45,7 @@ jobs:
       run: |
         pip install --upgrade pip
         pip install jupyter-book jupytext
-        pip install -r book/tinytorch-course/requirements.txt
+        pip install -r book/requirements.txt
         
     - name: Generate notebooks for Binder/Colab
       run: |
@@ -67,13 +67,13 @@ jobs:
         
     - name: Build the book
       run: |
-        cd book/tinytorch-course
+        cd book
         jupyter-book build . --all
         
     - name: Upload book artifact
       uses: actions/upload-pages-artifact@v3
       with:
-        path: book/tinytorch-course/_build/html
+        path: book/_build/html
 
   deploy:
     # Only deploy on main branch pushes (not PRs)