feat(tui): task-board preview frames (tasks / task-detail)

Add "tasks" and "task-detail" kinds to PreviewFrame, backed by a
sampleTaskBoard work graph that exercises every readiness glyph and
status color (epic blocked on children, a ready child, in-flight, done).

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

apps/tui-go/internal/app/demo.go

@@ -255,10 +255,56 @@ func PreviewFrame(kind string, w, h int) string {
 		}
 		m.grantIndex = 1
 		m.overlay = OverlayGrants
+
+	case "tasks", "task-detail":
+		m.connected = true
+		m.currentModel = "llama-cpp:default"
+		m.sessions = sampleSessions()
+		m.selectedID = "04a546aa"
+		m.overlay = OverlayTasks
+		m.taskList = sampleTaskBoard()
+		if kind == "task-detail" {
+			m.taskDetail = true
+			m.taskListIndex = 2 // a blocked child, to show the "waiting on" line
+		}
 	}
 	return m.render()
 }
 
+// sampleTaskBoard is a decomposed work graph: an epic waiting on its three
+// children, one of which (webui-2) is ready now, plus an in-flight and a done
+// task — exercising every readiness glyph and status color.
+func sampleTaskBoard() []TaskSummary {
+	return []TaskSummary{
+		{
+			ID: "webui-1", Key: "webui-1", Status: "TODO", Title: "Frontend web UI for correx",
+			Goal:      "operator can drive sessions from a browser",
+			BlockedBy: []string{"webui-2", "webui-3", "webui-4"},
+			Links:     []TaskLinkWire{{TargetID: "webui-2", Type: "DEPENDS_ON", TargetKind: "TASK"}},
+		},
+		{
+			ID: "webui-2", Key: "webui-2", Status: "TODO", Title: "Scaffold the Vite + React app",
+			Goal: "buildable shell with routing", Ready: true,
+			AcceptanceCriteria: []string{"npm run build passes", "lands under apps/web"},
+			AffectedPaths:      []string{"apps/web/"},
+		},
+		{
+			ID: "webui-3", Key: "webui-3", Status: "TODO", Title: "Auth / token entry view",
+			Goal: "operator pastes a token and connects", BlockedBy: []string{"webui-2"},
+			Links: []TaskLinkWire{{TargetID: "webui-1", Type: "IMPLEMENTS", TargetKind: "TASK"}},
+		},
+		{
+			ID: "webui-4", Key: "webui-4", Status: "TODO", Title: "Session board view",
+			Goal: "live roster mirroring the TUI", BlockedBy: []string{"webui-2"},
+		},
+		{
+			ID: "api-7", Key: "api-7", Status: "IN_PROGRESS", Title: "CORS + token endpoint",
+			Goal: "server accepts browser origins", Claimant: "04a546aa8b2c",
+		},
+		{ID: "api-3", Key: "api-3", Status: "DONE", Title: "Stable /sessions JSON shape"},
+	}
+}
+
 func sampleStats() *protocol.StatsDto {
 	return &protocol.StatsDto{
 		SessionID:         "04a546aa",