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/workflowpattern/trace_writer.go

@@ -3,16 +3,16 @@ package workflowpattern
 import "fmt"
 
 type TraceWriter interface {
-	Info(string, ...interface{})
+	Info(string, ...any)
 }
 
 type EmptyTraceWriter struct{}
 
-func (*EmptyTraceWriter) Info(string, ...interface{}) {
+func (*EmptyTraceWriter) Info(string, ...any) {
 }
 
 type StdOutTraceWriter struct{}
 
-func (*StdOutTraceWriter) Info(format string, args ...interface{}) {
+func (*StdOutTraceWriter) Info(format string, args ...any) {
 	fmt.Printf(format+"\n", args...)
 }

pkg/workflowpattern/workflow_pattern.go

@@ -34,7 +34,7 @@ func CompilePattern(rawpattern string) (*WorkflowPattern, error) {
 	}, nil
 }
 
-//nolint:gocyclo
+//nolint:gocyclo // function handles many cases
 func PatternToRegex(pattern string) (string, error) {
 	var rpattern strings.Builder
 	rpattern.WriteString("^")
@@ -127,7 +127,7 @@ func PatternToRegex(pattern string) (string, error) {
 			if errorMessage.Len() > 0 {
 				errorMessage.WriteString(", ")
 			}
-			errorMessage.WriteString(fmt.Sprintf("Position: %d Error: %s", position, err))
+			fmt.Fprintf(&errorMessage, "Position: %d Error: %s", position, err)
 		}
 		return "", fmt.Errorf("invalid Pattern '%s': %s", pattern, errorMessage.String())
 	}