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

cmd/relspec/merge_from_list_test.go

@@ -105,7 +105,7 @@ func TestRunMerge_FromListPathWithSpaces(t *testing.T) {
 	defer restoreMergeState(saved)
 
 	spacedDir := filepath.Join(t.TempDir(), "my schema files")
-	if err := os.MkdirAll(spacedDir, 0755); err != nil {
+	if err := os.MkdirAll(spacedDir, 0o755); err != nil {
 		t.Fatal(err)
 	}
 	targetFile := filepath.Join(spacedDir, "target schema.json")