make clean leaves tracked founder-pitch.pdf behind #41

What is wrong?

The clean target runs git clean -dfX, but founder-pitch.pdf is tracked in the repository while also listed in .gitignore. git clean never removes tracked files, so make clean leaves that generated artifact in place and a following make may skip rebuilding it even when the source or class changed.

Where?

• Makefile:17
• .gitignore:25
• Tracked founder-pitch.pdf

Reproduction

1. Check out the repository and note that founder-pitch.pdf is present and tracked.
2. Run make clean.
3. Verify that founder-pitch.pdf still exists.
4. Change founder-pitch.tex's mtime/content back to an older timestamp or change a non-prerequisite class/asset, then run make; the stale tracked PDF can remain untouched.

Expected behavior

make clean should remove generated PDFs (or tracked artifacts should not be treated as generated), and a clean build should regenerate both outputs.

Suggested fix

Stop tracking generated PDFs and let git clean -dfX remove them, or explicitly delete both PDF targets in the clean recipe and keep their dependency graph complete.