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/app/format_test.go

@@ -163,3 +163,14 @@ func TestDisplayOverlapPolicy(t *testing.T) {
 		t.Errorf("inherited policy = %q, want %q", got, want)
 	}
 }
+
+func TestDisplayTimeout(t *testing.T) {
+	own := domain.Job{TimeoutSeconds: 45}
+	if got, want := DisplayTimeout(own, 30), "45 s"; got != want {
+		t.Errorf("per-job timeout = %q, want %q", got, want)
+	}
+	inherit := domain.Job{TimeoutSeconds: 0}
+	if got, want := DisplayTimeout(inherit, 30), "30 s (global default)"; got != want {
+		t.Errorf("inherited timeout = %q, want %q", got, want)
+	}
+}