[taskboard] add task detail pages

app/api/tasks/[id]/route.ts

@@ -1,6 +1,24 @@
 import { NextResponse } from "next/server";
 
-import { updateTask, validateTaskPayload } from "@/lib/tasks";
+import { findTask, updateTask, validateTaskPayload } from "@/lib/tasks";
+
+export async function GET(
+  _request: Request,
+  { params }: { params: Promise<{ id: string }> },
+) {
+  const { id } = await params;
+  const numericId = Number(id);
+  if (!Number.isInteger(numericId) || numericId <= 0) {
+    return NextResponse.json({ error: "invalid_task_id" }, { status: 400 });
+  }
+
+  const task = await findTask(numericId);
+  if (!task) {
+    return NextResponse.json({ error: "task_not_found" }, { status: 404 });
+  }
+
+  return NextResponse.json(task);
+}
 
 export async function PATCH(
   request: Request,