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.go

@@ -285,7 +285,7 @@ func (w *Writer) generateFilename(data *TemplateData) (string, error) {
 }
 
 // writeOutput writes the output to a file or stdout
-func (w *Writer) writeOutput(content string, outputPath string) error {
+func (w *Writer) writeOutput(content, outputPath string) error {
 	// If output path is empty, write to stdout
 	if outputPath == "" {
 		fmt.Print(content)
@@ -295,13 +295,13 @@ func (w *Writer) writeOutput(content string, outputPath string) error {
 	// Ensure directory exists
 	dir := filepath.Dir(outputPath)
 	if dir != "." && dir != "" {
-		if err := os.MkdirAll(dir, 0755); err != nil {
+		if err := os.MkdirAll(dir, 0o755); err != nil {
 			return fmt.Errorf("failed to create directory %s: %w", dir, err)
 		}
 	}
 
 	// Write to file
-	if err := os.WriteFile(outputPath, []byte(content), 0644); err != nil {
+	if err := os.WriteFile(outputPath, []byte(content), 0o644); err != nil {
 		return fmt.Errorf("failed to write file %s: %w", outputPath, err)
 	}