Reorganize JAX intro lecture for improved pedagogical flow

Major restructuring:
- Move Functional Programming section earlier (after NumPy Replacement)
- Integrate pure functions discussion into Random Numbers section
- Move "Compiling non-pure functions" into JIT section
- Add smooth transitions between sections

This creates a logical progression: basics → philosophy → features
Readers now understand WHY before seeing HOW, making JAX's design
choices (like explicit random state) more intuitive.

Also fix syntax errors in timer code blocks (missing colons).

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

Co-Authored-By: Claude <[email protected]>

Author: jstac