feat: per-job command timeout with global default

Add an optional per-job run timeout following the overlap_policy inherit
pattern: Job.TimeoutSeconds (0 = inherit) resolves against a new
Config.DefaultTimeoutSeconds (default 30s), replacing the hard-coded 30s
guard in runner.RunJob.

- domain/storage: new fields, default 30, load-time normalization
- runner: RunJob takes an explicit timeout; StartOnly stays untimed so it
  keeps measuring launch latency only
- app: effectiveTimeout resolves under mu into runEnv, threaded to runJob;
  seam signature and validation updated; DisplayTimeout helper
- ui: Timeout entry in the job dialog, Default timeout in Settings, and a
  Timeout row in the details panel
- tests + docs (ARCHITECTURE, STANDARDS, ROADMAP, CHANGELOG) updated;
  version bumped to 0.12.0

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/storage/store.go

@@ -78,6 +78,8 @@ func loadOrCreateConfig(paths Paths) (domain.Config, error) {
 		NotifyOnFailure:   true,
 		ExecutionMode:     domain.ExecutionModeParallel,
 		OverlapPolicy:     domain.OverlapPolicySkip,
+
+		DefaultTimeoutSeconds: 30,
 	}
 
 	if _, err := os.Stat(paths.ConfigPath); errors.Is(err, os.ErrNotExist) {
@@ -112,6 +114,9 @@ func loadOrCreateConfig(paths Paths) (domain.Config, error) {
 	if config.OverlapPolicy == "" {
 		config.OverlapPolicy = domain.OverlapPolicySkip
 	}
+	if config.DefaultTimeoutSeconds <= 0 {
+		config.DefaultTimeoutSeconds = 30
+	}
 	return config, nil
 }