feat: integrate Pi backend and Pi Web

pi-web/app/api/sessions/route.ts

@@ -0,0 +1,15 @@
+import { NextResponse } from "next/server";
+import { listAllSessions } from "@/lib/session-reader";
+import { getRunningRpcSessionIds } from "@/lib/rpc-manager";
+
+export async function GET() {
+  try {
+    const sessions = await listAllSessions();
+    return NextResponse.json({ sessions, runningSessionIds: getRunningRpcSessionIds() });
+  } catch (error) {
+    return NextResponse.json(
+      { error: String(error) },
+      { status: 500 }
+    );
+  }
+}