ci: optimize docs workflow - auto-deploy to separate branch

[cc-hearts]

Summary

Optimized the documentation workflow to automatically deploy docs to a separate docs branch, removing docs from the main codebase to reduce PR size and improve CI efficiency.

Changes

1. .gitignore - Exclude docs directory

• Added docs to .gitignore

2. .github/workflows/doc.yaml - Optimized workflow

Key improvements:

• ✅ Only runs on main branch push (not on PRs)
• ✅ Added paths-ignore to skip unnecessary triggers
• ✅ Added permissions for better security
• ✅ Added timeout to prevent hanging jobs
• ✅ Improved commit message with [skip ci] to avoid CI loops

Trigger conditions:

on:
  push:
    branches:
      - main
    paths-ignore:
      - 'docs/**'
      - 'README.md'
      - 'README_ZH.md'
      - 'CHANGELOG.md'
      - 'LICENSE'
      - '.github/**'

3. Removed docs from git tracking

• Docs are now generated and deployed automatically by CI
• No more docs changes in PRs

Benefits

Before

• ❌ Every PR included large docs diffs (60+ files)
• ❌ Docs workflow ran on every PR (wasted CI resources)
• ❌ Manual docs management required

After

• ✅ PRs are clean and focused on code changes
• ✅ Docs auto-deploy only when main branch changes
• ✅ Docs are always up-to-date via CI
• ✅ Reduced PR review time

How it works

1. Developer pushes code to main
2. CI detects changes (ignores docs, README, etc.)
3. Doc workflow runs:
   • Installs dependencies
   • Generates documentation
   • Deploys to docs branch automatically
4. GitHub Pages (if configured) serves from docs branch

Breaking Changes

None. This is a CI/CD optimization only.