public/: replace symlinks with real files

The `tf` cross-deck symlinks (`hccs-{white,green}.png`, plot screenshots,
etc.) and abs-path symlinks (`agentic-*` from oa/automation) worked
locally but broke CI — the sibling repos aren't checked out there, so
Vite/Rolldown saw broken targets and `UNRESOLVED_IMPORT`-ed.

Real-copy only the assets actually referenced by `slides.md` (+ favicon).
Unused symlinks for slides that got deleted are also gone.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ryan-williams