configure CodeQL for Go 1.27

GitHub's managed CodeQL setup currently installs Go 1.26 and forces
`GOTOOLCHAIN=local`, so its autobuild cannot analyze a module targeting Go
1.27.

Move CodeQL to a repository workflow that installs the Go version from
`go.mod`. Use an explicit Go build for reliable extraction while retaining
the existing Go and GitHub Actions analyses and weekly schedule.

Author: bgentry

.github/workflows/codeql.yaml

@@ -0,0 +1,54 @@
+name: CodeQL
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+  schedule:
+    - cron: "17 4 * * 1"
+
+jobs:
+  analyze:
+    name: Analyze (${{ matrix.language }})
+    runs-on: ubuntu-latest
+    permissions:
+      actions: read
+      contents: read
+      packages: read
+      security-events: write
+
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - language: actions
+            build-mode: none
+          - language: go
+            build-mode: manual
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v7
+
+      - name: Setup Go
+        if: matrix.language == 'go'
+        uses: actions/setup-go@v7
+        with:
+          check-latest: true
+          go-version-file: "go.mod"
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v4
+        with:
+          build-mode: ${{ matrix.build-mode }}
+          languages: ${{ matrix.language }}
+
+      - name: Build Go
+        if: matrix.language == 'go'
+        run: go build ./...
+
+      - name: Perform CodeQL analysis
+        uses: github/codeql-action/analyze@v4
+        with:
+          category: "/language:${{ matrix.language }}"