chore: keep worktree model symlinks out of the tree

The fix pass ran in git worktrees, which need models/ symlinked in from the
main checkout to build. .gitignore covered the embedder and llm symlinks but
not stt and tts, so those two were committed as absolute-path symlinks.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TrVSBKe3RFDF4fGYKWYQnX

.gitignore

@@ -52,3 +52,5 @@ coverage.out
 
 # Agent worktrees and local agent state
 .claude/
+/models/stt
+/models/tts