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/ui/mainwindow_test.go

@@ -24,14 +24,15 @@ func newTestService(t *testing.T) *app.Service {
 			LogsDir:        filepath.Join(dir, "logs"),
 		},
 		Config: domain.Config{
-			JobsDir:         ".",
-			LogsDir:         "logs",
-			MaxLogFiles:     100,
-			MaxLogAgeDays:   30,
-			ExecutionMode:   domain.ExecutionModeParallel,
-			OverlapPolicy:   domain.OverlapPolicySkip,
-			KeepRunningInTray: true,
-			NotifyOnFailure:   true,
+			JobsDir:               ".",
+			LogsDir:               "logs",
+			MaxLogFiles:           100,
+			MaxLogAgeDays:         30,
+			ExecutionMode:         domain.ExecutionModeParallel,
+			OverlapPolicy:         domain.OverlapPolicySkip,
+			DefaultTimeoutSeconds: 30,
+			KeepRunningInTray:     true,
+			NotifyOnFailure:       true,
 		},
 	}
 	return app.NewService(store, nil)