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

vendor/golang.org/x/text/cases/context.go

@@ -249,7 +249,7 @@ func upper(c *context) bool {
 	return c.copy()
 }
 
-// isUpper writes the isUppercase version of the current rune to dst.
+// isUpper reports whether the current rune is in upper case.
 func isUpper(c *context) bool {
 	ct := c.caseType()
 	if c.info&hasMappingMask == 0 || ct == cUpper {