Fix download paths and add frontmatter downloads configuration

Fixes 404 errors for notebook downloads by:
- Correcting download paths in downloads.md to use relative paths (./notebooks/, ./learn_probability_notebooks.zip)
- Adding downloads configuration to frontmatter of all 30 notebook files
- Adding missing frontmatter to exercise and appendix files that didn't have it

This enables MyST's built-in download buttons to work correctly alongside the
custom downloads page. Each chapter now has a download button in the UI that
points to the correct .ipynb file location.

Author: claude

add_download_frontmatter.py

@@ -0,0 +1,88 @@
+#!/usr/bin/env python3
+"""
+Add downloads configuration to frontmatter of all notebook markdown files.
+"""
+
+import re
+from pathlib import Path
+
+def add_downloads_to_frontmatter(file_path):
+    """Add downloads configuration to a markdown file's frontmatter."""
+    with open(file_path, 'r') as f:
+        content = f.read()
+
+    # Extract the frontmatter
+    frontmatter_match = re.match(r'^---\n(.*?)\n---\n(.*)$', content, re.DOTALL)
+    if not frontmatter_match:
+        print(f"⚠️  No frontmatter found in {file_path}")
+        return False
+
+    frontmatter = frontmatter_match.group(1)
+    body = frontmatter_match.group(2)
+
+    # Check if downloads already exists
+    if 'downloads:' in frontmatter:
+        print(f"ℹ️  Downloads already configured in {file_path}")
+        return False
+
+    # Generate the ipynb filename
+    stem = file_path.stem
+    ipynb_file = f"notebooks/{stem}.ipynb"
+
+    # Add downloads configuration
+    downloads_config = f"\ndownloads:\n  - file: {ipynb_file}\n"
+    new_frontmatter = frontmatter + downloads_config
+
+    # Write back
+    new_content = f"---\n{new_frontmatter}---\n{body}"
+    with open(file_path, 'w') as f:
+        f.write(new_content)
+
+    print(f"✓ Added downloads to {file_path}")
+    return True
+
+def main():
+    """Add downloads configuration to all notebook files."""
+    print("=" * 60)
+    print("Adding Downloads Configuration to Frontmatter")
+    print("=" * 60)
+
+    # Get all markdown notebook files
+    files = []
+
+    # Chapter files
+    for i in range(1, 22):
+        file = Path(f"chapter_{i:02d}.md")
+        if file.exists():
+            files.append(file)
+
+    # Lab files
+    for lab_file in ["chapter_04_lab.md", "chapter_05_lab.md"]:
+        file = Path(lab_file)
+        if file.exists():
+            files.append(file)
+
+    # Exercise files
+    for exercise_file in ["chapter_04_exercises_a.md", "chapter_04_exercises_b.md"]:
+        file = Path(exercise_file)
+        if file.exists():
+            files.append(file)
+
+    # Appendix files
+    for letter in ['a', 'b', 'c', 'd', 'e']:
+        file = Path(f"appendix_{letter}.md")
+        if file.exists():
+            files.append(file)
+
+    print(f"\nProcessing {len(files)} files...\n")
+
+    updated = 0
+    for file in files:
+        if add_downloads_to_frontmatter(file):
+            updated += 1
+
+    print(f"\n✓ Updated {updated} files")
+    print("=" * 60)
+
+if __name__ == "__main__":
+    main()

appendix_a.md

@@ -9,6 +9,8 @@ kernelspec:
   display_name: Python 3 (ipykernel)
   language: python
   name: python3
+downloads:
+  - file: notebooks/appendix_a.ipynb
 ---
 
 # Appendix A: Python/Jupyter Setup Deep Dive

appendix_b.md

@@ -9,6 +9,8 @@ kernelspec:
   display_name: Python 3 (ipykernel)
   language: python
   name: python3
+downloads:
+  - file: notebooks/appendix_b.ipynb
 ---
 
 # Appendix B: Essential Library Reference

appendix_c.md

@@ -9,6 +9,8 @@ kernelspec:
   display_name: Python 3 (ipykernel)
   language: python
   name: python3
+downloads:
+  - file: notebooks/appendix_c.ipynb
 ---
 
 # Appendix C: Mathematical Notation Summary

appendix_d.md

@@ -9,6 +9,8 @@ kernelspec:
   display_name: Python 3 (ipykernel)
   language: python
   name: python3
+downloads:
+  - file: notebooks/appendix_d.ipynb
 ---
 
 # Appendix D: Further Reading and Resources

appendix_e.md

@@ -1,3 +1,18 @@
+---
+jupytext:
+  text_representation:
+    extension: .md
+    format_name: myst
+    format_version: 0.13
+    jupytext_version: 1.18.1
+kernelspec:
+  display_name: Python 3 (ipykernel)
+  language: python
+  name: python3
+downloads:
+  - file: notebooks/appendix_e.ipynb
+---
+
 # Appendix E: Summary of Formulas
 
 This appendix provides a summary of the key formulas introduced in Chapters 1–8.

chapter_01.md

@@ -9,6 +9,8 @@ kernelspec:
   display_name: Python 3 (ipykernel)
   language: python
   name: python3
+downloads:
+  - file: notebooks/chapter_01.ipynb
 ---
 
 # Chapter 1: Introduction to Probability and Python Setup

chapter_02.md

@@ -9,6 +9,8 @@ kernelspec:
   display_name: Python 3 (ipykernel)
   language: python
   name: python3
+downloads:
+  - file: notebooks/chapter_02.ipynb
 ---
 
 # Chapter 2: The Language of Probability: Sets, Sample Spaces, and Events

chapter_03.md

@@ -9,6 +9,8 @@ kernelspec:
   display_name: Python 3 (ipykernel)
   language: python
   name: python3
+downloads:
+  - file: notebooks/chapter_03.ipynb
 ---
 
 # Chapter 3: Counting Techniques: Permutations and Combinations

chapter_04.md

@@ -9,6 +9,8 @@ kernelspec:
   display_name: Python 3 (ipykernel)
   language: python
   name: python3
+downloads:
+  - file: notebooks/chapter_04.ipynb
 ---
 
 # Chapter 4: Conditional Probability