feat: redesign complet de l'application basé sur les maquettes Stitch

Refonte du design system (CSS variables, composants glass/card/button/badge),
nouvelle page PodcastDetails avec route /podcast/:id,
lecteur audio immersif avec visualiseur audio,
animations, thème dark/light, responsive mobile/desktop.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/services/episodeService.ts

@@ -75,4 +75,14 @@ export const episodeService = {
     const response = await api.get(`/episodes/progress/${episodeId}`);
     return response.data;
   },
+
+  searchEpisodes: async (
+    query: string,
+    limit: number = 40
+  ): Promise<EpisodeResponse> => {
+    const response = await api.get('/episodes/search', {
+      params: { q: query, limit },
+    });
+    return response.data;
+  },
 };