fix(ci): add HF_TOKEN and model caching, remove uv.lock

[HumanBean17]

Summary

• Add HF_TOKEN environment variable to CI workflow for authenticated HuggingFace downloads
• Add HuggingFace model caching to avoid repeated downloads and HTTP 429 errors
• Set TRANSFORMERS_CACHE and HF_HOME environment variables for consistent model paths
• Remove uv.lock that was accidentally committed in rollback commit
• Add uv.lock to .gitignore to prevent future commits

Problem

CI was failing with HTTP 429 rate limiting errors from HuggingFace when loading the sentence-transformers/all-MiniLM-L6-v2 model during tests. The model was being downloaded repeatedly without authentication or caching.

Solution

1. Added HF_TOKEN from GitHub secrets for authenticated requests (higher rate limits)
2. Added HuggingFace model caching using GitHub Actions cache
3. Set proper cache environment variables (TRANSFORMERS_CACHE, HF_HOME)
4. Removed accidentally committed uv.lock file
5. Added uv.lock to .gitignore

Test plan

• CI passes with the new HF_TOKEN and caching configuration
• No more HTTP 429 errors from HuggingFace

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