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>

models/user/user.go

@@ -20,8 +20,6 @@ import (
 	"time"
 	"unicode"
 
-	_ "image/jpeg" // Needed for jpeg support
-
 	"code.gitea.io/gitea/models/auth"
 	"code.gitea.io/gitea/models/db"
 	"code.gitea.io/gitea/modules/auth/openid"
@@ -39,6 +37,8 @@ import (
 	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/modules/validation"
 
+	_ "image/jpeg" // Needed for jpeg support
+
 	"golang.org/x/text/runes"
 	"golang.org/x/text/transform"
 	"golang.org/x/text/unicode/norm"