docs: note codeql coverage

.github/workflows/codeql.yml

@@ -0,0 +1,38 @@
+name: CodeQL
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+      - ci/codeql-control-gates
+  schedule:
+    - cron: "43 4 * * 1"
+  workflow_dispatch:
+
+permissions:
+  actions: read
+  contents: read
+  security-events: write
+
+jobs:
+  analyze:
+    name: analyze
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - name: Setup Go
+        uses: actions/setup-go@v6
+        with:
+          go-version-file: go.mod
+          cache: true
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v4
+        with:
+          languages: go
+
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@v4

CHANGELOG.md

@@ -14,6 +14,8 @@
 
 ### Maintenance
 
+- Add CodeQL analysis on pull requests, `main`, the CI preview branch, weekly
+  schedule, and manual dispatch.
 - Document the read-only `metadata --json`, `status --json`, and
   `doctor --json` control surface for launchers, automation, and CI checks.