ci: add GitHub Actions for image builds, PR checks and security scans

- dev-images: build/push backend, worker, frontend to ghcr.io and Docker
  Hub on every push to dev (tags: dev, dev-<sha>)
- release-images: same images on v* tag push (tags: latest, <version>)
- PR checks (into main/dev): ruff lint+format, eslint+prettier, no-push
  Docker build of all targets
- CodeQL (python, js/ts), dependency-review, pip-audit, npm audit, Trivy fs
- pin .github/workflows/*.yml to LF

.github/workflows/codeql.yml

@@ -0,0 +1,48 @@
+name: CodeQL
+
+# Static analysis of the Python and JS/TS code for security and quality issues.
+# Results appear under the repository's Security -> Code scanning tab.
+
+on:
+  push:
+    branches: [main, dev]
+  pull_request:
+    branches: [main, dev]
+  schedule:
+    - cron: "27 3 * * 1" # weekly, Monday 03:27 UTC
+
+concurrency:
+  group: codeql-${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  analyze:
+    name: Analyze (${{ matrix.language }})
+    runs-on: ubuntu-latest
+    permissions:
+      security-events: write
+      actions: read
+      contents: read
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - language: python
+          - language: javascript-typescript
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v3
+        with:
+          languages: ${{ matrix.language }}
+          build-mode: none
+
+      - name: Perform CodeQL analysis
+        uses: github/codeql-action/analyze@v3
+        with:
+          category: "/language:${{ matrix.language }}"