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/pgsql/extensions.go

@@ -247,7 +247,8 @@ var extensionFunctionPrefixes = buildExtensionIndex(func(ext Extension) []string
 
 func buildExtensionIndex(keys func(Extension) []string) map[string]string {
 	index := make(map[string]string)
-	for _, ext := range postgresExtensions {
+	for name := range postgresExtensions {
+		ext := postgresExtensions[name]
 		for _, key := range keys(ext) {
 			// Deterministic on collision: the alphabetically first extension wins.
 			if existing, ok := index[key]; ok && existing < ext.Name {