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>

cmd/notices.go

@@ -76,7 +76,7 @@ func getVersionNotices(version string) []Notice {
 	noticeURL.RawQuery = query.Encode()
 
 	client := &http.Client{}
-	req, err := http.NewRequest("GET", noticeURL.String(), nil)
+	req, err := http.NewRequest(http.MethodGet, noticeURL.String(), nil)
 	if err != nil {
 		log.Debug(err)
 		return nil
@@ -102,7 +102,7 @@ func getVersionNotices(version string) []Notice {
 
 	defer resp.Body.Close()
 	notices := []Notice{}
-	if resp.StatusCode == 304 {
+	if resp.StatusCode == http.StatusNotModified {
 		log.Debug("No new notices")
 		return nil
 	}