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

backend/src/db/schema.ts

@@ -38,6 +38,14 @@ export interface ProgressNote {
   note: string;
 }
 
+export interface Subtask {
+  id: string;
+  title: string;
+  completed: boolean;
+  completedAt?: string;
+  createdAt: string;
+}
+
 // ─── Projects ───
 
 export interface ProjectLink {
@@ -73,6 +81,8 @@ export const tasks = pgTable("tasks", {
   assigneeId: text("assignee_id"),
   assigneeName: text("assignee_name"),
   projectId: uuid("project_id").references(() => projects.id, { onDelete: "set null" }),
+  dueDate: timestamp("due_date", { withTimezone: true }),
+  subtasks: jsonb("subtasks").$type<Subtask[]>().default([]),
   progressNotes: jsonb("progress_notes").$type<ProgressNote[]>().default([]),
   createdAt: timestamp("created_at", { withTimezone: true }).defaultNow().notNull(),
   updatedAt: timestamp("updated_at", { withTimezone: true }).defaultNow().notNull(),