feat: add GitHub Actions support

- Copy .gitea/ to .github/ for GitHub Actions compatibility
- Update .github/workflows to use GITHUB_SERVER_URL/GITHUB_REPOSITORY
- Update main.go to accept both GITEA_* and GITHUB_* env vars

Works on both Gitea and GitHub without code changes.

.github/workflows/pr-ready-gate.yml

@@ -0,0 +1,38 @@
+name: PR Ready Gate
+
+on:
+  pull_request:
+    types: [synchronize]
+
+jobs:
+  clear-labels:
+    runs-on: ubuntu-24.04
+    # Always run - curl commands are safe if labels don't exist
+    steps:
+      - name: Remove ready and self-reviewed labels, reassign to author
+        env:
+          GITEA_TOKEN: ${{ secrets.RODIN_TOKEN }}
+        run: |
+          PR_NUMBER=${{ github.event.pull_request.number }}
+          AUTHOR=${{ github.event.pull_request.user.login }}
+          READY_LABEL_ID=38
+          SELF_REVIEWED_LABEL_ID=37
+          
+          # Remove ready label if present
+          curl -sS -X DELETE \
+            -H "Authorization: token $GITEA_TOKEN" \
+            "https://gitea.weiker.me/api/v1/repos/${{ github.repository }}/issues/${PR_NUMBER}/labels/${READY_LABEL_ID}" || true
+          
+          # Remove self-reviewed label if present
+          curl -sS -X DELETE \
+            -H "Authorization: token $GITEA_TOKEN" \
+            "https://gitea.weiker.me/api/v1/repos/${{ github.repository }}/issues/${PR_NUMBER}/labels/${SELF_REVIEWED_LABEL_ID}" || true
+          
+          # Reassign to author
+          curl -sS -X PATCH \
+            -H "Authorization: token $GITEA_TOKEN" \
+            -H "Content-Type: application/json" \
+            -d "{\"assignees\": [\"${AUTHOR}\"]}" \
+            "https://gitea.weiker.me/api/v1/repos/${{ github.repository }}/pulls/${PR_NUMBER}"
+          
+          echo "Cleared ready/self-reviewed labels and reassigned PR #${PR_NUMBER} to ${AUTHOR}"