Repo spring cleaning (#746)

- Add CI workflow (pytest + frontend typecheck/tests) on PRs
- Add CodeQL static analysis for Python and JS/TS
- Add Dependabot for pip, npm, Docker, and GitHub Actions
- Tighten workflow permissions

.github/workflows/codeql.yml

@@ -0,0 +1,38 @@
+name: CodeQL
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+  schedule:
+    - cron: "0 6 * * 1" # Weekly on Monday at 6am UTC
+
+permissions:
+  contents: read
+
+jobs:
+  analyze:
+    runs-on: ubuntu-latest
+    permissions:
+      security-events: write
+    strategy:
+      fail-fast: false
+      matrix:
+        language: [python, javascript-typescript]
+    steps:
+      - name: Checkout
+        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@820e3160e279568db735cee8ed8f8e77a6da7818 # v3
+        with:
+          languages: ${{ matrix.language }}
+
+      - name: Autobuild
+        uses: github/codeql-action/autobuild@820e3160e279568db735cee8ed8f8e77a6da7818 # v3
+
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@820e3160e279568db735cee8ed8f8e77a6da7818 # v3
+        with:
+          category: "/language:${{ matrix.language }}"