docs: Add GitHub Actions CI/CD workflow for GitHub Pages

[shouze]

Context

Parent epic: #24
Depends on: #25 (VitePress initialized)

Workflow: .github/workflows/docs.yml

Triggers

on:
  push:
    branches: [main]
    paths:
      - "docs/**"
      - ".github/workflows/docs.yml"
  workflow_dispatch:

Job: build

- uses: oven-sh/setup-bun@v2
  with:
    bun-version: latest
- run: bun install --frozen-lockfile
- run: bun run docs:build
- uses: actions/upload-pages-artifact@v3
  with:
    path: docs/.vitepress/dist

Job: deploy (depends on build)

permissions:
  pages: write
  id-token: write
environment:
  name: github-pages
  url: ${{ steps.deployment.outputs.page_url }}
steps:
  - uses: actions/deploy-pages@v4
    id: deployment

Tasks

• Create .github/workflows/docs.yml with the above structure
• Enable GitHub Pages in repo Settings → Pages → Source: GitHub Actions
• Verify the workflow runs successfully on merge to main
• Verify the site is live at https://fulll.github.io/github-code-search/
• Add a docs badge to the slim README (docs: Slim down README.md (keep install + link to docs) #32)

Acceptance criteria

• Merging a PR touching docs/** auto-triggers a deployment
• The site is accessible at https://fulll.github.io/github-code-search/
• The workflow uses only official GitHub Actions and oven-sh/setup-bun — no third-party deploy service
• Build + deploy completes in < 3 minutes
• Workflow can also be triggered manually via workflow_dispatch