ci: replace settings-generated CodeQL job with containerized workflow

.github/workflows/codeql.yml

@@ -0,0 +1,49 @@
+# This workflow replaces the repository-settings-generated CodeQL setup.
+# Running the job in a container avoids workspace permission issues on
+# self-hosted runners and keeps the build environment fully isolated.
+name: CodeQL
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+  schedule:
+    - cron: '0 6 * * 1'
+
+jobs:
+  analyze:
+    name: Analyze (cpp)
+    runs-on: self-hosted
+
+    container:
+      image: buildpack-deps:jammy
+
+    defaults:
+      run:
+        shell: bash
+
+    permissions:
+      actions: read
+      contents: read
+      security-events: write
+
+    steps:
+      - name: Configure Git safe directory
+        run: git config --global --add safe.directory '*'
+
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v4
+        with:
+          languages: cpp
+
+      - name: Build
+        run: |
+          make clean || true  # tolerate missing or no-op clean target
+          make -j"$(nproc)"
+
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@v4