docs: add VitePress documentation site

- Add docs directory with VitePress configuration
- Add GitHub Actions workflow for docs build and deploy
- Support bilingual (English/Chinese) documentation
- Include search, custom theme, and responsive design

.github/workflows/docs.yml

@@ -0,0 +1,105 @@
+name: Docs Build & Deploy
+
+on:
+  push:
+    branches:
+      - main
+      - develop
+    paths:
+      - 'docs/**'
+  pull_request:
+    branches:
+      - main
+      - develop
+    paths:
+      - 'docs/**'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: "pages"
+  cancel-in-progress: false
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: docs
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          cache: 'npm'
+          cache-dependency-path: docs/package-lock.json
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Build
+        run: npm run docs:build
+
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: docs/.vitepress/dist
+
+  deploy:
+    if: github.event_name == 'push' && github.ref == 'refs/heads/main'
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    runs-on: ubuntu-latest
+    needs: build
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4
+
+  # Lighthouse CI for PRs
+  lighthouse:
+    if: github.event_name == 'pull_request'
+    runs-on: ubuntu-latest
+    needs: build
+    defaults:
+      run:
+        working-directory: docs
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          cache: 'npm'
+          cache-dependency-path: docs/package-lock.json
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Build
+        run: npm run docs:build
+
+      - name: Start preview server
+        run: |
+          npm run docs:preview -- --host 127.0.0.1 --port 4173 &
+          npx --yes wait-on http://127.0.0.1:4173/
+
+      - name: Run Lighthouse CI
+        uses: treosh/lighthouse-ci-action@v10
+        with:
+          urls: |
+            http://127.0.0.1:4173/
+          uploadArtifacts: true
+          temporaryPublicStorage: true
+          commentPR: true
+          budgetPath: docs/lighthouse-budget.json