feat: Apply fixes for type errors and unused variables

frontend/src/App.tsx

@@ -1,4 +1,3 @@
-import React from 'react';
 import './app/globals.css';
 import RootLayout from './app/layout';
 import Home from './app/page';

frontend/src/app/page.tsx

@@ -1,4 +1,3 @@
-import React from "react";
 import FeedList from "../components/FeedList";
 import EpisodePlayer from "../components/EpisodePlayer";
 

frontend/src/components/EpisodePlayer.tsx

@@ -1,6 +1,4 @@
-"use client";
-
-import React, { useEffect, useState } from "react";
+import { useEffect, useState } from "react";
 
 interface Episode {
   id: string;
@@ -13,7 +11,6 @@ interface Episode {
 export default function EpisodePlayer() {
   const [episodes, setEpisodes] = useState<Episode[]>([]);
   const [selectedEpisode, setSelectedEpisode] = useState<Episode | null>(null);
-  const [isPlaying, setIsPlaying] = useState(false);
   const [audioUrl, setAudioUrl] = useState<string | null>(null);
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState<string | null>(null);

frontend/src/components/FeedList.tsx

@@ -1,8 +1,4 @@
-"use client";
-
-"use client";
-
-import React, { useEffect, useState } from "react";
+import { useEffect, useState } from "react";
 
 interface FeedItem {
   id: string;