feat: add CI/CD workflow with linting, building, and docker

Add GitHub Actions workflow that performs linting with golangci-lint,
formats check, cross-compilation for linux/amd64, linux/arm64, and
windows/amd64, and multi-platform docker image publishing to Gitea
registry on pushes to main/master branches.

.github/workflows/ci-cd.yml

@@ -0,0 +1,79 @@
+name: CI/CD
+
+on:
+  push:
+    branches: [main, master]
+  pull_request:
+    branches: [main, master]
+
+jobs:
+  lint-and-format:
+    name: Lint & Format
+    runs-on: shell-ubuntu
+    steps:
+      - name: Checkout repo
+        run: git clone "$GITEA_CLONE_URL" .
+
+      - name: Download dependencies
+        run: go mod download
+
+      - name: Install golangci-lint
+        run: curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b /usr/local/bin v1.64.8
+
+      - name: Run golangci-lint
+        run: golangci-lint run --timeout=3m
+
+      - name: Check formatting
+        run: |
+          if [ "$(gofmt -l $(find . -name '*.go' -not -path './vendor/*'))" ]; then
+            echo "Files not properly formatted:"
+            gofmt -l $(find . -name '*.go' -not -path './vendor/*')
+            exit 1
+          fi
+
+  build:
+    name: Build binaries
+    runs-on: shell-ubuntu
+    needs: lint-and-format
+    steps:
+      - name: Checkout repo
+        run: git clone "$GITEA_CLONE_URL" .
+
+      - name: Build for Linux amd64
+        run: CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -o auth-gate-linux-amd64 .
+
+      - name: Build for Linux arm64
+        run: CGO_ENABLED=0 GOOS=linux GOARCH=arm64 go build -o auth-gate-linux-arm64 .
+
+      - name: Build for Windows amd64
+        run: CGO_ENABLED=0 GOOS=windows GOARCH=amd64 go build -o auth-gate-windows-amd64.exe
+
+      - name: Package binaries
+        run: |
+          tar czf auth-gate-linux-amd64.tar.gz auth-gate-linux-amd64
+          tar czf auth-gate-linux-arm64.tar.gz auth-gate-linux-arm64
+          tar czf auth-gate-windows-amd64.tar.gz auth-gate-windows-amd64.exe
+
+  docker:
+    name: Build & push Docker image
+    runs-on: shell-ubuntu
+    needs: lint-and-format
+    if: github.event_name == 'push'
+    steps:
+      - name: Checkout repo
+        run: git clone "$GITEA_CLONE_URL" .
+
+      - name: Login to Gitea Registry
+        run: echo "${{ secrets.GITEA_TOKEN }}" | docker login git.yejayekhoob.com -u "${{ secrets.GITEA_USERNAME }}" --password-stdin
+
+      - name: Set up Docker Buildx
+        run: docker buildx create --name builder --use
+
+      - name: Build & push
+        run: |
+          docker buildx build \
+            --platform linux/amd64,linux/arm64 \
+            --tag "git.yejayekhoob.com/db123/auth-gate:${{ github.sha }}" \
+            --tag "git.yejayekhoob.com/db123/auth-gate:latest" \
+            --push \
+            .