ci: overhaul pipeline — caching, GoReleaser, govulncheck

- Add module + build cache to CI (was only caching go-build, not go/pkg/mod)
- Declare explicit Alpine container instead of relying on runner image
- Drop redundant go vet (already in golangci-lint)
- Add govulncheck job for dependency CVE scanning
- Add GoReleaser config for Gitea-native binary releases + checksums
- Replace .github/workflows/docker.yml with .gitea/workflows/release.yml
- Docker multiarch (amd64+arm64) via buildx in release workflow
- Dockerfile: add --mount=type=cache for mod/build, add -trimpath

.github/workflows/docker.yml

@@ -1,47 +0,0 @@
-name: Publish Release
-
-on:
-  push:
-    tags:
-      - '[0-9]*'
-
-jobs:
-  push_to_registry:
-    name: Build and Push Docker Image
-    runs-on: ubuntu-latest
-    steps:
-      - name: Check out the repo
-        uses: actions/checkout@v4
-
-      - name: Set up QEMU
-        uses: docker/setup-qemu-action@v3
-
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
-
-      - name: Log in to Docker Hub
-        uses: docker/login-action@v3
-        with:
-          username: ${{ secrets.DOCKERHUB_USERNAME }}
-          password: ${{ secrets.DOCKERHUB_TOKEN }}
-
-      - name: Extract metadata (tags, labels)
-        id: meta
-        uses: docker/metadata-action@v5
-        with:
-          images: ${{ secrets.DOCKERHUB_USERNAME }}/uptop
-          tags: |
-            type=match,pattern=\d+\.\d+\.\d+
-            type=raw,value=latest
-
-      - name: Build and push
-        uses: docker/build-push-action@v5
-        with:
-          context: .
-          push: true
-          tags: ${{ steps.meta.outputs.tags }}
-          labels: ${{ steps.meta.outputs.labels }}
-          build-args: |
-            VERSION=${{ github.ref_name }}
-            COMMIT=${{ github.sha }}
-            BUILD_DATE=${{ github.event.head_commit.timestamp }}