feat: due dates, subtasks, and task detail page (HQ-{number} URLs)

- Schema: added due_date and subtasks JSONB columns to tasks
- API: CRUD endpoints for subtasks (/tasks/:id/subtasks)
- API: due date support in create/update task
- TaskDetailPanel: due date picker with overdue/soon badges
- TaskDetailPanel: subtask checklist with progress bar
- TaskPage: full-page task view at /task/HQ-{number}
- Dashboard: task cards link to detail page, show subtask progress & due date badges
- Migration: 0001_mighty_callisto.sql

frontend/src/App.tsx

@@ -4,6 +4,7 @@ import { DashboardPage } from "./pages/DashboardPage";
 import { QueuePage } from "./pages/QueuePage";
 import { ChatPage } from "./pages/ChatPage";
 import { ProjectsPage } from "./pages/ProjectsPage";
+import { TaskPage } from "./pages/TaskPage";
 import { AdminPage } from "./components/AdminPage";
 import { LoginPage } from "./components/LoginPage";
 import { useSession } from "./lib/auth-client";
@@ -15,6 +16,7 @@ function AuthenticatedApp() {
         <Route element={<DashboardLayout />}>
           <Route path="/" element={<DashboardPage />} />
           <Route path="/queue" element={<QueuePage />} />
+          <Route path="/task/:taskRef" element={<TaskPage />} />
           <Route path="/projects" element={<ProjectsPage />} />
           <Route path="/chat" element={<ChatPage />} />
           <Route path="/admin" element={<AdminPage />} />