feat: add Gitea workflows for selective GitHub mirroring

- Add three different approaches for mirroring to GitHub
- Approach 1: Filter out sensitive files on a separate branch
- Approach 2: Use git archive with .gitattributes exclusions
- Approach 3: Use rsync for flexible file filtering
- Add exclusion lists for sensitive files and directories
- Protect production configs, environment files, and private data

This allows maintaining a public GitHub mirror while keeping
sensitive configuration and data private on the Gitea instance.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

.gitea/workflows/mirror-to-github.yml

@@ -0,0 +1,48 @@
+name: Mirror to GitHub
+
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  mirror:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+        with:
+          fetch-depth: 0  # Full history needed for mirroring
+
+      - name: Setup Git
+        run: |
+          git config --global user.name "Gitea Mirror Bot"
+          git config --global user.email "bot@noreply.gitea.local"
+
+      - name: Create filtered branch
+        run: |
+          # Create a new branch for GitHub
+          git checkout -b github-mirror
+          
+          # Remove sensitive files/directories
+          # Example: Remove .env files, private configs, etc.
+          git rm -r --cached .env* || true
+          git rm -r --cached backend/.env* || true
+          git rm -r --cached frontend/.env* || true
+          git rm -r --cached docker-compose.prod.yml || true
+          git rm -r --cached .claudedocs/ || true
+          git rm -r --cached backend/data/ || true
+          git rm -r --cached backend/storage/ || true
+          
+          # Commit the changes
+          git commit -m "Remove sensitive files for GitHub mirror" || true
+
+      - name: Push to GitHub
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          # Add GitHub remote
+          git remote add github https://x-access-token:${GITHUB_TOKEN}@github.com/YOUR_GITHUB_USERNAME/YOUR_REPO_NAME.git
+          
+          # Force push the filtered branch to GitHub main
+          git push github github-mirror:main --force