feat(m9): todo/kanban with DnD, assignee notify, completion, tests, e2e

- TodoRepository (column CRUD, item CRUD, soft-delete, ordering, maxOrderIndex,
  project isolation) + TodoService (lazy standard-column init, member/admin
  permission, create/update/move/toggleComplete/delete, todo_assigned notify,
  todo_created/updated/completed activity logs, SSE todo.updated)
- APIs: columns + items (GET/POST/PATCH/DELETE), toggleComplete + move
- KanbanBoard client (HTML5 drag&drop move, new task per column, complete),
  todos page, ProjectNav ToDo link
- Unit tests (TodoRepository, TodoService) + e2e todo-kanban

app/projects/[projectId]/todos/page.tsx

@@ -0,0 +1,49 @@
+import { redirect } from 'next/navigation';
+import { getCurrentUser, toPublicUser } from '@/lib/auth/getCurrentUser';
+import { createTodoService, createProjectService } from '@/lib/api/services';
+import { Header } from '@/components/layout/Header';
+import { ProjectNav } from '@/components/layout/ProjectNav';
+import { KanbanBoard } from '@/components/todo/KanbanBoard';
+import { ForbiddenError, NotFoundError } from '@/lib/errors';
+
+export const dynamic = 'force-dynamic';
+
+export default async function TodosPage({
+  params,
+}: {
+  params: Promise<{ projectId: string }>;
+}) {
+  const user = await getCurrentUser();
+  if (!user) redirect('/login');
+  const { projectId } = await params;
+
+  const projectService = createProjectService();
+  let project: Awaited<ReturnType<typeof projectService.getProject>>;
+  try {
+    project = projectService.getProject(user.id, Number(projectId));
+  } catch (error) {
+    if (error instanceof ForbiddenError || error instanceof NotFoundError) {
+      redirect('/dashboard');
+    }
+    throw error;
+  }
+
+  const todoService = createTodoService();
+  const columns = todoService.getColumns(user.id, project.id);
+  const items = todoService.getItems(user.id, project.id);
+
+  return (
+    <div className="min-h-screen bg-gray-50">
+      <Header user={toPublicUser(user)} />
+      <ProjectNav projectId={project.id} active="todos" />
+      <main className="space-y-4 p-6">
+        <h1 className="text-2xl font-bold">ToDo / Kanban</h1>
+        <KanbanBoard
+          projectId={project.id}
+          columns={columns}
+          initialItems={items}
+        />
+      </main>
+    </div>
+  );
+}