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/api/projects/[projectId]/todos/items/route.ts

@@ -0,0 +1,60 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { getCurrentUser } from '@/lib/auth/getCurrentUser';
+import { createTodoService } from '@/lib/api/services';
+import { UnauthorizedError } from '@/lib/errors';
+import { handleApiError, jsonError } from '@/lib/api/handleError';
+
+export const runtime = 'nodejs';
+
+export async function GET(
+  _request: NextRequest,
+  { params }: { params: Promise<{ projectId: string }> }
+) {
+  const user = await getCurrentUser();
+  if (!user) return handleApiError(new UnauthorizedError());
+  const { projectId } = await params;
+  const service = createTodoService();
+  try {
+    return NextResponse.json({
+      items: service.getItems(user.id, Number(projectId)),
+    });
+  } catch (error) {
+    return handleApiError(error);
+  }
+}
+
+export async function POST(
+  request: NextRequest,
+  { params }: { params: Promise<{ projectId: string }> }
+) {
+  const user = await getCurrentUser();
+  if (!user) return handleApiError(new UnauthorizedError());
+  const { projectId } = await params;
+  let body: Record<string, unknown>;
+  try {
+    body = (await request.json()) as Record<string, unknown>;
+  } catch {
+    return jsonError(400, 'リクエスト本文が不正です');
+  }
+  const service = createTodoService();
+  try {
+    const item = service.createItem(user.id, Number(projectId), {
+      title: String(body.title ?? ''),
+      columnId: Number(body.columnId ?? 0),
+      description:
+        typeof body.description === 'string' ? body.description : undefined,
+      assigneeId:
+        body.assigneeId === null || body.assigneeId === undefined
+          ? null
+          : Number(body.assigneeId),
+      priority:
+        typeof body.priority === 'string'
+          ? (body.priority as 'low' | 'normal' | 'high')
+          : undefined,
+      dueDate: typeof body.dueDate === 'string' ? body.dueDate : null,
+    });
+    return NextResponse.json({ item }, { status: 201 });
+  } catch (error) {
+    return handleApiError(error);
+  }
+}