Add CI and manual image publishing workflows

- .gitea/workflows/ci.yml: on every push/PR, run Django checks + the full
  backend suite against MariaDB/Redis services and the frontend
  lint/type-check/build. Runs on the nitro-ci runner (ubuntu-latest).
- .gitea/workflows/publish.yml: manual dispatch; multi-arch build+push of
  both images as :latest and :<short-sha> with GIT_HASH baked in.
- push_*.sh: non-interactive registry login for CI (REGISTRY_USER/
  REGISTRY_TOKEN) and a PLATFORMS override.

.gitea/workflows/ci.yml

@@ -0,0 +1,114 @@
+# J621 CI — runs on every push (and pull request): Django checks + the full
+# backend test suite against MariaDB/Redis, and the frontend type-check,
+# lint and production build.
+#
+# Runner: the "nitro-ci" act_runner with the custom `ubuntu-latest` label.
+
+name: CI
+
+on:
+  push:
+    branches: ["**"]
+    tags-ignore: ["**"]
+  pull_request:
+  workflow_dispatch:
+
+concurrency:
+  group: ci-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  backend:
+    name: Backend tests
+    runs-on: ubuntu-latest
+    services:
+      mariadb:
+        image: mariadb:11.4
+        env:
+          MARIADB_ROOT_PASSWORD: root
+          MARIADB_DATABASE: j621
+          MARIADB_USER: j621
+          MARIADB_PASSWORD: j621
+        options: >-
+          --health-cmd "healthcheck.sh --connect --innodb_initialized"
+          --health-interval 5s
+          --health-timeout 5s
+          --health-retries 20
+      redis:
+        image: redis:7-alpine
+        options: >-
+          --health-cmd "redis-cli ping"
+          --health-interval 5s
+          --health-timeout 5s
+          --health-retries 20
+    env:
+      DB_HOST: mariadb
+      DB_PORT: "3306"
+      DB_NAME: j621
+      DB_USER: j621
+      DB_PASSWORD: j621
+      DB_ROOT_PASSWORD: root
+      REDIS_URL: redis://redis:6379/1
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.14"
+          cache: pip
+          cache-dependency-path: backend/requirements.txt
+
+      - name: Install backend dependencies
+        run: pip install -r backend/requirements.txt
+
+      - name: Install a MariaDB client
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y --no-install-recommends default-mysql-client
+
+      - name: Grant the test database rights
+        run: |
+          for i in $(seq 1 30); do
+            mysql -h "$DB_HOST" -P "$DB_PORT" -u root -p"$DB_ROOT_PASSWORD" \
+              -e "SELECT 1" >/dev/null 2>&1 && break
+            sleep 2
+          done
+          mysql -h "$DB_HOST" -P "$DB_PORT" -u root -p"$DB_ROOT_PASSWORD" \
+            -e "GRANT ALL ON \`test_j621\`.* TO 'j621'@'%'; FLUSH PRIVILEGES;"
+
+      - name: Django system checks
+        working-directory: backend
+        run: python manage.py check
+
+      - name: Backend tests
+        working-directory: backend
+        run: >-
+          python manage.py test
+          apps.core.tests
+          apps.library.tests
+          apps.follows.tests
+          apps.accounts.tests
+
+  frontend:
+    name: Frontend build & lint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: "22"
+          cache: npm
+          cache-dependency-path: frontend/package-lock.json
+
+      - name: Install frontend dependencies
+        working-directory: frontend
+        run: npm ci
+
+      - name: Lint
+        working-directory: frontend
+        run: npm run lint
+
+      - name: Type-check & build
+        working-directory: frontend
+        run: npm run build

.gitea/workflows/publish.yml

@@ -0,0 +1,51 @@
+# J621 image publishing — manual workflow.
+#
+# Builds the backend (gunicorn + whitenoise, ffmpeg) and frontend (static
+# nginx) images for linux/amd64 + linux/arm64 and pushes them to the Gitea
+# registry as :latest and :<short-sha>, with the commit baked in as GIT_HASH.
+#
+# Run it from the Actions tab ("Run workflow"), or:
+#   curl -X POST .../api/v1/repos/JakeBreath/J621/actions/workflows/publish.yml/dispatches \
+#        -d '{"ref":"main"}'
+#
+# Registry login uses the automatic GITHUB_TOKEN (the repo needs package write
+# access for the actor); no extra secrets are required.
+
+name: Publish images
+
+on:
+  workflow_dispatch:
+    inputs:
+      platforms:
+        description: Build platforms (comma separated)
+        required: false
+        default: linux/amd64,linux/arm64
+
+concurrency:
+  group: publish
+  cancel-in-progress: false
+
+jobs:
+  publish:
+    name: Build & push images
+    runs-on: ubuntu-latest
+    env:
+      REGISTRY_USER: ${{ github.actor }}
+      REGISTRY_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      PLATFORMS: ${{ inputs.platforms || 'linux/amd64,linux/arm64' }}
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Register binfmt (multi-arch builds)
+        run: docker run --privileged --rm tonistiigi/binfmt --install all
+
+      - name: Build & push both images
+        run: |
+          set -euo pipefail
+          SHA="$(git rev-parse --short HEAD)"
+          echo "Publishing $SHA for $PLATFORMS"
+          # Both scripts honour REGISTRY_USER/REGISTRY_TOKEN (see deploy/push_*.sh).
+          PLATFORMS="$PLATFORMS" ./deploy/push_frontend.sh "$SHA"
+          PLATFORMS="$PLATFORMS" ./deploy/push_backend.sh "$SHA"