ci: add backend gitea build workflow

Add a Gitea Actions pipeline to compile the backend server artifact and build/push Docker images for master/dev changes.

Made-with: Cursor

.gitea/workflows/build.yml

@@ -0,0 +1,78 @@
+name: Build Backend
+
+on:
+  push:
+    branches:
+      - master
+      - dev
+  pull_request:
+    branches:
+      - master
+      - dev
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: '1.25'
+          cache: false
+
+      - name: Install build tools
+        run: sudo apt-get update && sudo apt-get install -y gcc
+
+      - name: Download dependencies
+        run: go mod download
+
+      - name: Build
+        env:
+          GOOS: linux
+          GOARCH: amd64
+          CGO_ENABLED: 1
+        run: go build -v -o server ./cmd/server
+
+      - name: Upload artifacts
+        uses: actions/upload-artifact@v3
+        with:
+          name: backend-server-linux-amd64
+          path: server
+
+  build-docker:
+    runs-on: ubuntu-latest
+    needs: build
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Login to Gitea Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: code.littlelan.cn
+          username: ${{ secrets.GIT_USERNAME }}
+          password: ${{ secrets.GIT_TOKEN }}
+
+      - name: Download artifact
+        uses: actions/download-artifact@v3
+        with:
+          name: backend-server-linux-amd64
+
+      - name: Ensure binary executable
+        run: chmod +x ./server
+
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: true
+          tags: |
+            code.littlelan.cn/carrot_bbs/backend:latest
+            code.littlelan.cn/carrot_bbs/backend:${{ github.sha }}
+          platforms: linux/amd64