feat(ci): Add GitHub Actions workflow for PRs (gt-pre9o)

Add .github/workflows/ci.yml with:
- .beads/ change detection to protect issue database
- Go build and test with race detection
- golangci-lint for code quality

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -0,0 +1,73 @@
+name: CI
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  # Fast check to catch accidental .beads/issues.jsonl changes from contributors
+  check-no-beads-changes:
+    name: Check for .beads changes
+    runs-on: ubuntu-latest
+    if: github.event_name == 'pull_request'
+    steps:
+      - uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+
+      - name: Check for .beads/issues.jsonl changes
+        run: |
+          if git diff --name-only origin/${{ github.base_ref }}...HEAD | grep -q "^\.beads/issues\.jsonl$"; then
+            echo "This PR includes changes to .beads/issues.jsonl"
+            echo ""
+            echo "This file is the project's issue database and should not be modified in PRs."
+            echo ""
+            echo "To fix, run:"
+            echo "  git checkout origin/main -- .beads/issues.jsonl"
+            echo "  git commit --amend"
+            echo "  git push --force"
+            echo ""
+            exit 1
+          fi
+          echo "No .beads/issues.jsonl changes detected"
+
+  test:
+    name: Test
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: '1.24'
+
+      - name: Configure Git
+        run: |
+          git config --global user.name "CI Bot"
+          git config --global user.email "ci@gastown.test"
+
+      - name: Build
+        run: go build -v ./cmd/gt
+
+      - name: Test
+        run: go test -v -race -short ./...
+
+  lint:
+    name: Lint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: '1.24'
+
+      - name: golangci-lint
+        uses: golangci/golangci-lint-action@v9
+        with:
+          version: latest
+          args: --timeout=5m