chore(ci): add govulncheck, staticcheck, go vet, gofumpt gates

* Add lint/format checks to the Gitea release workflow and Makefile
  (targets: vet, fmt, fmt-check, staticcheck, govulncheck, check)
* Switch .golangci.json formatter from gofmt to gofumpt (extra.group-params)
* Bump golang.org/x/text 0.37.0 -> 0.39.0 for GO-2026-5970; re-vendor
* Fix staticcheck S1011 in pkg/diff; drop unused pgsql writer helpers
* Fix gocritic unnamedResult (pkg/diff) and rangeValCopy (pkg/pgsql)
* Apply gofumpt + goimports formatting across the tree

.gitea/workflows/release.yml

@@ -20,12 +20,32 @@ jobs:
         with:
           go-version-file: go.mod
 
+      - name: go vet
+        run: go vet ./...
+
+      - name: gofumpt (golangci-lint fmt)
+        run: |
+          go install github.com/golangci/golangci-lint/v2/cmd/golangci-lint@latest
+          diff=$(golangci-lint fmt --diff 2>&1)
+          if [ -n "$diff" ]; then
+            echo "$diff"
+            echo "Formatting issues found. Run: make fmt"
+            exit 1
+          fi
+
+      - name: staticcheck
+        run: |
+          go install honnef.co/go/tools/cmd/staticcheck@latest
+          staticcheck ./...
+
+      - name: govulncheck
+        run: |
+          go install golang.org/x/vuln/cmd/govulncheck@latest
+          govulncheck ./...
+
       - name: Test
         run: go test ./...
 
-      - name: Lint
-        run: go vet ./...
-
   release:
     needs: test
     runs-on: ubuntu-latest