fix: stabilize GitHub Pages documentation workflow

[orangeboyChen]

Summary

• isolate VitePress from the root Tailwind PostCSS configuration
• use frozen docs dependency installation
• build docs on pull requests and deploy only after pushes to main

Validation

• bun run docs:build
• bun run lint
• bun run format:check
• bun run typecheck
• bun run test:coverage

The previous Pages failure was caused by the protected github-pages environment rejecting deployments from a feature branch; PR runs now validate the build without attempting deployment.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.77%. Comparing base (f3c94cb) to head (b836082).
⚠️ Report is 3 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #105   +/-   ##
=======================================
  Coverage   94.77%   94.77%           
=======================================
  Files          21       21           
  Lines        4251     4251           
  Branches     1238     1238           
=======================================
  Hits         4029     4029           
  Misses        222      222           

Flag	Coverage Δ
unittests	94.77% <ø> (ø)

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[chatgpt-codex-connector]

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