fix: add CodeQL workflow to replace Default setup

The CodeQL "Default setup" configured via GitHub UI was causing
"2 configurations not found" warnings on PRs because the
/language:actions and /language:python configurations on main
couldn't be matched on PR branches. Adding an explicit workflow
file ensures consistent CodeQL analysis across all branches.

https://claude.ai/code/session_0183rfcNCEDFZcGrvrUbb97h

Author: claude

.github/workflows/codeql.yml

@@ -0,0 +1,42 @@
+name: "CodeQL"
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+  schedule:
+    - cron: "25 14 * * 1"
+
+permissions:
+  security-events: write
+  contents: read
+  actions: read
+
+jobs:
+  analyze:
+    name: Analyze (${{ matrix.language }})
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - language: python
+            build-mode: none
+          - language: actions
+            build-mode: none
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v6
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v3
+        with:
+          languages: ${{ matrix.language }}
+          build-mode: ${{ matrix.build-mode }}
+
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@v3
+        with:
+          category: "/language:${{matrix.language}}"