Add .forgejo/workflows/build.yml: vet, test, cross-compile to windows/amd64

Two jobs: 'test' runs go vet + go test -race + a Linux smoke build to
catch generic compile errors cheaply. 'build-windows' cross-compiles
drover.exe with version metadata baked in and uploads it as an artifact
with 14-day retention. CGO is disabled - divert-go integration in a
later phase will switch it on with mingw.

Manual git clone (no actions/checkout/setup-go) because the runner's
golang:1.23-bookworm image lacks Node.js. Both jobs cache GOMODCACHE
and GOCACHE keyed by go.sum hash. Concurrency cancel-in-progress keeps
the queue tidy when commits land in quick succession.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.forgejo/workflows/build.yml

@@ -0,0 +1,83 @@
+name: Build
+
+on:
+  push:
+    branches: [main]
+    paths-ignore:
+      - 'docs/**'
+      - 'README.md'
+      - 'LICENSE'
+      - '*.md'
+  pull_request:
+    paths-ignore:
+      - 'docs/**'
+      - '*.md'
+
+concurrency:
+  group: build-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  test:
+    runs-on: go
+    steps:
+      - name: Checkout
+        run: |
+          git clone --no-checkout "https://forgejo-runner:${GITHUB_TOKEN}@git.okcu.io/${GITHUB_REPOSITORY}.git" /tmp/src
+          git -C /tmp/src checkout "$GITHUB_SHA"
+          cp -a /tmp/src/. .
+      - name: Cache Go modules
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cache/go-build
+            ~/go/pkg/mod
+          key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+          restore-keys: ${{ runner.os }}-go-
+      - name: Vet
+        run: go vet ./...
+      - name: Test with race
+        run: go test -race -coverprofile=coverage.txt -covermode=atomic ./...
+      - name: Linux smoke build
+        run: |
+          mkdir -p bin
+          go build -trimpath -ldflags="-s -w" -o bin/drover ./cmd/drover
+
+  build-windows:
+    runs-on: go
+    needs: test
+    steps:
+      - name: Checkout
+        run: |
+          git clone --no-checkout "https://forgejo-runner:${GITHUB_TOKEN}@git.okcu.io/${GITHUB_REPOSITORY}.git" /tmp/src
+          git -C /tmp/src checkout "$GITHUB_SHA"
+          cp -a /tmp/src/. .
+      - name: Cache Go modules
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cache/go-build
+            ~/go/pkg/mod
+          key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+          restore-keys: ${{ runner.os }}-go-
+      - name: Cross-compile drover.exe (windows/amd64)
+        env:
+          GOOS: windows
+          GOARCH: amd64
+          CGO_ENABLED: '0'
+        run: |
+          SHORT_SHA="${GITHUB_SHA:0:7}"
+          BUILD_DATE="$(date -u +%Y-%m-%d)"
+          mkdir -p bin
+          go build -trimpath -ldflags="-s -w \
+            -X main.Version=dev-${SHORT_SHA} \
+            -X main.Commit=${SHORT_SHA} \
+            -X main.BuildDate=${BUILD_DATE}" \
+            -o bin/drover.exe ./cmd/drover
+          ls -la bin/
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: drover-windows-amd64-${{ github.sha }}
+          path: bin/drover.exe
+          retention-days: 14