Update golangci-lint to v2.12.2 with canonical config

- Add canonical .golangci.yml (v2 schema, default: all, project
  thresholds for lll/funlen/cyclop/dupl)
- Bump golangci-lint pins from v2.0.2 to v2.12.2 in Makefile
  (go install, new /v2 module path) and Dockerfile (tagged+digest
  Debian image pin)
- Fix all lint findings surfaced by the new linter set across
  cmd/mfer, internal/bork, internal/cli, internal/log, and mfer:
  static sentinel errors (err113), context-aware HTTP and exec
  (noctx), guarded integer conversions and stricter permissions
  (gosec), named constants (mnd, goconst), function decomposition
  (funlen, cyclop, gocognit, nestif), declaration ordering
  (funcorder), t.Parallel/t.TempDir/t.Setenv adoption in tests
  (paralleltest, usetesting), protobuf getters (protogetter), plus
  formatting and style cleanups (wsl_v5, nlreturn, lll, revive,
  testifylint, and others)
- Serialize CLI runs in tests behind a mutex so parallel tests do
  not cross-wire the process-global logger's captured output

internal/cli/list.go

@@ -42,10 +42,11 @@ func (mfa *CLIApp) listManifestOperation(ctx *cli.Context) error {
 
 	for _, f := range files {
 		if longFormat {
-			mtime := time.Unix(f.Mtime.Seconds, int64(f.Mtime.Nanos))
-			_, _ = fmt.Fprintf(mfa.Stdout, "%d\t%s\t%s%s", f.Size, mtime.Format(time.RFC3339), f.Path, lineEnd)
+			mtime := time.Unix(f.GetMtime().GetSeconds(), int64(f.GetMtime().GetNanos()))
+			_, _ = fmt.Fprintf(mfa.Stdout, "%d\t%s\t%s%s",
+				f.GetSize(), mtime.Format(time.RFC3339), f.GetPath(), lineEnd)
 		} else {
-			_, _ = fmt.Fprintf(mfa.Stdout, "%s%s", f.Path, lineEnd)
+			_, _ = fmt.Fprintf(mfa.Stdout, "%s%s", f.GetPath(), lineEnd)
 		}
 	}