ci: add CodeQL workflow for code scanning (#316)

The main branch ruleset requires CodeQL results but no workflow existed
to produce them, blocking all PR merges.

Author: notgitika

.github/workflows/codeql.yml

@@ -0,0 +1,32 @@
+name: CodeQL
+
+on:
+  push:
+    branches: ['main']
+  pull_request:
+    branches: ['main']
+
+# Cancel in-progress runs when a new commit is pushed
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  analyze:
+    name: Analyze
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    permissions:
+      security-events: write
+      contents: read
+
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v3
+        with:
+          languages: javascript-typescript
+
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@v3