ci(codeql): advanced setup that skips proving-ground tasks and fixtures

.github/codeql/codeql-config.yml

@@ -0,0 +1,10 @@
+name: Sigil CodeQL
+
+# CodeQL covers the code Sigil ships: the CLI, the site and the workflows. Proving-ground tasks are
+# deliberately flawed starting repos, hidden verifiers and reference solutions that only ever run
+# inside the lab sandbox, and fixtures are test data; flagging them is noise that grows with every
+# suite. Capabilities are scanned by Sigil's own scanner in CI ("Scan the catalog").
+paths-ignore:
+  - tasks
+  - site/fixtures
+  - packages/sigil/test/fixtures

.github/workflows/codeql.yml

@@ -0,0 +1,40 @@
+name: CodeQL
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+  schedule:
+    - cron: "27 4 * * 1"
+
+permissions:
+  contents: read
+
+concurrency:
+  group: codeql-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  analyze:
+    name: Analyze (${{ matrix.language }})
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+    permissions:
+      contents: read
+      security-events: write
+    strategy:
+      fail-fast: false
+      matrix:
+        language: [actions, javascript-typescript]
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - uses: github/codeql-action/init@9b3254085494b55a0f7c4c2b3d2d52cc712ce370 # v4.39.1
+        with:
+          languages: ${{ matrix.language }}
+          build-mode: none
+          config-file: ./.github/codeql/codeql-config.yml
+      - uses: github/codeql-action/analyze@9b3254085494b55a0f7c4c2b3d2d52cc712ce370 # v4.39.1
+        with:
+          category: /language:${{ matrix.language }}