feat(chart): add a read-only natal chart page

Open /chart from the sidebar without billing or a model. Five tabs; Western and Qizheng stay unavailable until those endpoints land. Ephemeris nav points at /ephemeris (404 until that page ships).

frontend/src/app/api/chart-view/route.ts

@@ -0,0 +1,11 @@
+import { NextResponse } from "next/server";
+
+import { loadChartView } from "@/lib/chart-view-service";
+
+export const runtime = "nodejs";
+export const maxDuration = 60;
+
+export async function GET() {
+  const result = await loadChartView();
+  return NextResponse.json(result.body, { status: result.httpStatus });
+}