perf: replace goheader linter with custom check (#37599)

Replace the [slow `goheader` linter](https://github.com/denis-tingaikin/go-header/issues/70) with a
custom check.

Local go lint time is down from 247s to 32s. 6 new files that were
previously undetected because of `//go:build ignore` are fixed. The exit
code of the make target preserves the golangci-lint exit code, if
present.

Also refactors and consolidates the linting targets.

Signed-off-by: silverwind <me@silverwind.io>
Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>

models/db/driver_sqlite_mattn.go

@@ -1,8 +1,8 @@
-//go:build sqlite_mattn && sqlite_unlock_notify
-
 // Copyright 2026 The Gitea Authors. All rights reserved.
 // SPDX-License-Identifier: MIT
 
+//go:build sqlite_mattn && sqlite_unlock_notify
+
 package db
 
 import (

models/db/driver_sqlite_modernc.go

@@ -1,8 +1,8 @@
-//go:build !sqlite_mattn
-
 // Copyright 2026 The Gitea Authors. All rights reserved.
 // SPDX-License-Identifier: MIT
 
+//go:build !sqlite_mattn
+
 // modernc driver is chosen as the default one (compared to mattn, ncruces)
 // * mattn was used as default, but it requires CGO
 // * the CI times are almost the same for these three (race detector must be disabled)