Add Chapters 3 and 4 to Jupyter Book

Chapter 3: Plot Elements and Coordinate Systems
- Primitives and containers (Artist objects)
- Ordering with zorder
- Coordinate systems and transformations
- Window extents and multi-colored titles

Chapter 4: Text and Titles
- Simple titles and text placement
- Text formatting for numbers
- Legends with customization options
- Annotations with arrows
- Multi-colored titles and custom fonts

Converted all PDF figures to PNG format at 300 DPI

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: alexanderthclark

jupyterbook/_toc.yml

@@ -32,4 +32,8 @@ parts:
   - file: chapter1/index
     title: Chapter 1 - The Object-oriented Interface
   - file: chapter2/index
-    title: Chapter 2 - Axes Appearance, Ticks, and Grids
+    title: Chapter 2 - Axes Appearance, Ticks, and Grids
+  - file: chapter3/index
+    title: Chapter 3 - Plot Elements and Coordinate Systems
+  - file: chapter4/index
+    title: Chapter 4 - Text and Titles