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/pgsql/writer.go

@@ -1579,11 +1579,6 @@ func indexOperatorClassForColumn(col *models.Column, indexType, comment string)
 	}
 }
 
-// ginOperatorClassForColumn is the GIN-specific form of indexOperatorClassForColumn.
-func ginOperatorClassForColumn(col *models.Column, comment string) string {
-	return indexOperatorClassForColumn(col, "gin", comment)
-}
-
 func operatorClassCompatible(method, baseType string, isArray bool, opClass string) bool {
 	if vectorType, ok := vectorOperatorClasses[opClass]; ok {
 		return !isArray && baseType == vectorType && isVectorIndexMethod(method)
@@ -1604,10 +1599,6 @@ func operatorClassCompatible(method, baseType string, isArray bool, opClass stri
 	}
 }
 
-func ginOperatorClassCompatible(baseType string, isArray bool, opClass string) bool {
-	return operatorClassCompatible("gin", baseType, isArray, opClass)
-}
-
 func isTextGinBaseType(baseType string) bool {
 	switch baseType {
 	case "text", "varchar", "character varying", "char", "character", "string", "citext", "bpchar":
@@ -1793,15 +1784,6 @@ func nativeGistBaseType(baseType string) bool {
 	return strings.HasSuffix(baseType, "range") || strings.HasSuffix(baseType, "multirange")
 }
 
-func schemaRequiresPGTrgm(schema *models.Schema) bool {
-	for _, ext := range requiredExtensions(schema) {
-		if ext == "pg_trgm" {
-			return true
-		}
-	}
-	return false
-}
-
 func resolveIndexColumn(table *models.Table, colName string) (*models.Column, bool) {
 	if table == nil {
 		return nil, false