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/export.go

@@ -41,21 +41,24 @@ func (mfa *CLIApp) exportManifestOperation(ctx *cli.Context) error {
 
 	for _, f := range files {
 		entry := ExportEntry{
-			Path:   f.Path,
-			Size:   f.Size,
-			Hashes: make([]string, 0, len(f.Hashes)),
+			Path:   f.GetPath(),
+			Size:   f.GetSize(),
+			Hashes: make([]string, 0, len(f.GetHashes())),
 		}
 
-		for _, h := range f.Hashes {
-			entry.Hashes = append(entry.Hashes, hex.EncodeToString(h.MultiHash))
+		for _, h := range f.GetHashes() {
+			entry.Hashes = append(entry.Hashes, hex.EncodeToString(h.GetMultiHash()))
 		}
 
-		if f.Mtime != nil {
-			t := time.Unix(f.Mtime.Seconds, int64(f.Mtime.Nanos)).UTC().Format(time.RFC3339Nano)
+		if f.GetMtime() != nil {
+			t := time.Unix(f.GetMtime().GetSeconds(), int64(f.GetMtime().GetNanos())).
+				UTC().Format(time.RFC3339Nano)
 			entry.Mtime = &t
 		}
-		if f.Ctime != nil {
-			t := time.Unix(f.Ctime.Seconds, int64(f.Ctime.Nanos)).UTC().Format(time.RFC3339Nano)
+
+		if f.GetCtime() != nil {
+			t := time.Unix(f.GetCtime().GetSeconds(), int64(f.GetCtime().GetNanos())).
+				UTC().Format(time.RFC3339Nano)
 			entry.Ctime = &t
 		}
 
@@ -64,7 +67,9 @@ func (mfa *CLIApp) exportManifestOperation(ctx *cli.Context) error {
 
 	enc := json.NewEncoder(mfa.Stdout)
 	enc.SetIndent("", "  ")
-	if err := enc.Encode(entries); err != nil {
+
+	err = enc.Encode(entries)
+	if err != nil {
 		return fmt.Errorf("export: failed to encode JSON: %w", err)
 	}