feat: add AssetItem API routes

src/app/api/assets/route.ts

@@ -0,0 +1,53 @@
+import { NextResponse } from "next/server";
+import { auth } from "@/auth";
+import { createAssetItem, listAssetItems, validateCreateAssetItemInput } from "@/lib/assets";
+
+// Mirrors src/app/api/employees/route.ts's pattern — middleware.ts excludes
+// /api from route protection, so this checks the session itself. Flat
+// permission model (CLAUDE.md): only "logged in or not", no role check.
+export async function POST(request: Request): Promise<NextResponse> {
+  const session = await auth();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  let body: unknown;
+  try {
+    body = await request.json();
+  } catch {
+    return NextResponse.json({ error: "Request body must be valid JSON" }, { status: 400 });
+  }
+
+  if (typeof body !== "object" || body === null) {
+    return NextResponse.json({ error: "Request body must be a JSON object" }, { status: 400 });
+  }
+
+  const { serialNumber, model, purchaseDate, warrantyEndDate } = body as Record<string, unknown>;
+  const validation = validateCreateAssetItemInput({
+    serialNumber,
+    model,
+    purchaseDate,
+    warrantyEndDate,
+  });
+
+  if (!validation.ok) {
+    return NextResponse.json({ error: validation.error }, { status: 400 });
+  }
+
+  const created = await createAssetItem(validation.value);
+  if (!created.ok) {
+    return NextResponse.json({ error: created.error }, { status: 400 });
+  }
+
+  return NextResponse.json(created.value, { status: 201 });
+}
+
+export async function GET(): Promise<NextResponse> {
+  const session = await auth();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  const assetItems = await listAssetItems();
+  return NextResponse.json(assetItems, { status: 200 });
+}