ci: add CodeQL, pre-commit, and labeler workflows

- CodeQL: Python security analysis on push/PR + weekly schedule
- Pre-commit: ruff lint/format checks on push/PR
- Labeler: auto-label PRs based on changed files

.github/workflows/codeql.yml

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