Replace custom Go formatter with golangci-lint fmt (#37194)

Use `golangci-lint fmt` to format code, replacing the previous custom
formatter tool. https://github.com/daixiang0/gci is used to order the
imports.

`make fmt` performs ~13% faster while consuming ~57% less cpu while
formatting for me.

`GOFUMPT_PACKAGE` is gone because it's using the builtin package from
golangci-lint.

Co-authored-by: Claude (claude-opus-4-6) <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/web/web.go

@@ -45,7 +45,7 @@ import (
 	"code.gitea.io/gitea/services/context"
 	"code.gitea.io/gitea/services/forms"
 
-	_ "code.gitea.io/gitea/modules/session" // to registers all internal adapters
+	_ "code.gitea.io/gitea/modules/session" // to register all internal adapters
 
 	"gitea.com/go-chi/captcha"
 	chi_middleware "github.com/go-chi/chi/v5/middleware"