feat: org-scoped tasks backend, wire tasks page

Add the tasks table, validation, service and routes (/api/tasks with a
PATCH for partial updates / the done toggle, RBAC-gated) and the frontend
data module. The tasks board now loads, creates and toggles real data
(optimistic toggle with rollback).

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

backend/src/types/task.ts

@@ -0,0 +1,17 @@
+// The canonical Task shape returned by the API. Mirrors the frontend
+// `lib/tasks.ts` Task type. Scoped to the active clinic (a shared care-team
+// to-do board). `patient` is an optional free-text reference for context.
+export type TaskPriority = "high" | "medium" | "low";
+
+export type Task = {
+  id: string;
+  title: string;
+  assignee: string;
+  due: string;
+  priority: TaskPriority;
+  patient: string | null;
+  notes: string | null;
+  done: boolean;
+  createdAt: string;
+  updatedAt: string;
+};