Add Gitea CI to build and push images to docker.sejong.dev.

Switch compose to pull sejong-office:latest and document registry secrets and deploy steps.

Co-authored-by: Cursor <cursoragent@cursor.com>

.gitea/workflows/ci.yml

@@ -0,0 +1,61 @@
+name: CI
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  build:
+    name: Type-check & Build
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: "22"
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Type-check and build
+        run: npm run build
+
+  image:
+    name: Build & Push image
+    needs: build
+    if: github.event_name == 'push' && github.ref == 'refs/heads/main'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to registry
+        uses: docker/login-action@v3
+        with:
+          registry: docker.sejong.dev
+          username: ${{ secrets.REGISTRY_USERNAME }}
+          password: ${{ secrets.REGISTRY_PASSWORD }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          push: true
+          tags: |
+            docker.sejong.dev/sejong-office:latest
+            docker.sejong.dev/sejong-office:sha-${{ github.sha }}
+
+      - name: Log out of registry
+        if: always()
+        run: docker logout docker.sejong.dev