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/assetloader/loader_test.go

@@ -137,7 +137,10 @@ func TestScanDir_OrdersByPriorityThenSequence(t *testing.T) {
 		t.Fatalf("expected 4 items, got %d", len(items))
 	}
 
-	type ps struct{ p int; s uint }
+	type ps struct {
+		p int
+		s uint
+	}
 	want := []ps{{1, 1}, {1, 2}, {2, 1}, {2, 2}}
 	for i, w := range want {
 		got := ps{items[i].Priority, items[i].Sequence}