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

pkg/writers/template/writer_test.go

@@ -17,10 +17,10 @@ func TestWriterTableIndexValuesDeterministic(t *testing.T) {
 	outputPath := filepath.Join(outputDir, "accounts.txt")
 	templateBody := "{{range values .Table.Indexes}}{{.Name}}:{{join .Columns \",\"}}\n{{end}}"
 
-	if err := os.MkdirAll(outputDir, 0755); err != nil {
+	if err := os.MkdirAll(outputDir, 0o755); err != nil {
 		t.Fatalf("create output dir: %v", err)
 	}
-	if err := os.WriteFile(templatePath, []byte(templateBody), 0644); err != nil {
+	if err := os.WriteFile(templatePath, []byte(templateBody), 0o644); err != nil {
 		t.Fatalf("write template: %v", err)
 	}