Use golangci-lint fmt to format code (#163)

Use `golangci-lint fmt` to format code, upgrading `.golangci.yml` to v2 and mirroring the linter configuration used by https://github.com/go-gitea/gitea. `gci` now handles import ordering into standard, project-local, blank, and default groups.

Mirrors https://github.com/go-gitea/gitea/pull/37194.

Changes:
- Upgrade `.golangci.yml` to v2 format with the same linter set as gitea (minus `prealloc`, `unparam`, `testifylint`, `nilnil` which produced too many pre-existing issues)
- Add path-based exclusions (`bodyclose`, `gosec` in tests; `gosec:G115`/`G117` globally)
- Run lint via `make lint-go` in CI instead of `golangci/golangci-lint-action`, matching the pattern used by other Gitea repos
- Apply safe auto-fixes (`modernize`, `perfsprint`, `usetesting`, etc.)
- Add explanations to existing `//nolint` directives
- Remove dead code (unused `newRemoteReusableWorkflow` and `networkName`), duplicate imports, and shadowed `max` builtins
- Replace deprecated `docker/distribution/reference` with `distribution/reference`
- Fix `Deprecated:` comment casing and simplify nil/len checks

---
This PR was written with the help of Claude Opus 4.7

Reviewed-on: https://gitea.com/gitea/act/pulls/163
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-committed-by: silverwind <me@silverwind.io>

pkg/common/file.go

@@ -7,7 +7,7 @@ import (
 )
 
 // CopyFile copy file
-func CopyFile(source string, dest string) (err error) {
+func CopyFile(source, dest string) (err error) {
 	sourcefile, err := os.Open(source)
 	if err != nil {
 		return err
@@ -30,11 +30,11 @@ func CopyFile(source string, dest string) (err error) {
 		}
 	}
 
-	return
+	return err
 }
 
 // CopyDir recursive copy of directory
-func CopyDir(source string, dest string) (err error) {
+func CopyDir(source, dest string) (err error) {
 	// get properties of source dir
 	sourceinfo, err := os.Stat(source)
 	if err != nil {