Traduit l'UI en français et corrige les bugs de recherche/abonnement

- Traduit toutes les pages et composants en français (Dashboard, Login, Discover, Navigation, Header, EpisodeCard, AudioPlayer)
- Corrige l'erreur 500 sur /api/podcasts/discover : z.coerce.number() au lieu de z.number() pour limit/offset (paramètres query string)
- Corrige l'abonnement manuel via URL RSS : crée le podcast depuis le flux RSS au lieu de renvoyer 400

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/AudioPlayer.tsx

@@ -133,7 +133,7 @@ export default function AudioPlayer({ episode, onClose, userId }: AudioPlayerPro
       {/* Header */}
       <div className="sticky top-0 bg-white/80 backdrop-blur-xl border-b border-light-200">
         <div className="max-w-4xl mx-auto px-4 py-4 flex items-center justify-between">
-          <h2 className="text-xl font-bold text-light-900">Now Playing</h2>
+          <h2 className="text-xl font-bold text-light-900">En cours de lecture</h2>
           <button
             onClick={onClose}
             className="p-2 hover:bg-light-100 rounded-lg transition-colors"
@@ -163,7 +163,7 @@ export default function AudioPlayer({ episode, onClose, userId }: AudioPlayerPro
         {/* Info */}
         <div className="text-center mb-8">
           <p className="text-sm font-semibold text-light-500 uppercase mb-2">
-            {podcast?.author || 'Unknown Podcast'}
+            {podcast?.author || 'Podcast inconnu'}
           </p>
           <h1 className="text-4xl font-bold text-light-900 mb-3">{episode.title}</h1>
           <p className="text-light-600 line-clamp-3">{episode.description}</p>
@@ -195,7 +195,7 @@ export default function AudioPlayer({ episode, onClose, userId }: AudioPlayerPro
               }
             }}
             className="p-3 hover:bg-light-100 rounded-full transition-colors"
-            title="Rewind 15s"
+            title="Reculer de 15s"
           >
             <SkipBack className="w-6 h-6" />
           </button>
@@ -220,7 +220,7 @@ export default function AudioPlayer({ episode, onClose, userId }: AudioPlayerPro
               }
             }}
             className="p-3 hover:bg-light-100 rounded-full transition-colors"
-            title="Skip 30s"
+            title="Avancer de 30s"
           >
             <SkipForward className="w-6 h-6" />
           </button>
@@ -230,7 +230,7 @@ export default function AudioPlayer({ episode, onClose, userId }: AudioPlayerPro
         <div className="grid grid-cols-2 gap-6">
           {/* Playback Speed */}
           <div className="card">
-            <h3 className="text-sm font-semibold text-light-900 mb-3">Speed</h3>
+            <h3 className="text-sm font-semibold text-light-900 mb-3">Vitesse</h3>
             <div className="flex gap-2">
               {[0.75, 1, 1.25, 1.5, 1.75, 2].map((speed) => (
                 <button

frontend/src/components/EpisodeCard.tsx

@@ -8,7 +8,7 @@ interface EpisodeCardProps {
 
 export default function EpisodeCard({ episode, onPlay }: EpisodeCardProps) {
   const podcast = typeof episode.podcastId === 'object' ? episode.podcastId : null;
-  const pubDate = new Date(episode.pubDate).toLocaleDateString('en-US', {
+  const pubDate = new Date(episode.pubDate).toLocaleDateString('fr-FR', {
     month: 'short',
     day: 'numeric',
   });
@@ -45,7 +45,7 @@ export default function EpisodeCard({ episode, onPlay }: EpisodeCardProps) {
 
         {/* Podcast Title */}
         <p className="text-xs font-semibold text-light-500 uppercase tracking-wider mb-1">
-          {podcast?.author || 'Unknown'}
+          {podcast?.author || 'Inconnu'}
         </p>
 
         {/* Episode Title */}

frontend/src/components/Header.tsx

@@ -47,7 +47,7 @@ export default function Header({ title, subtitle, user, onLogout }: HeaderProps)
                   onClick={onLogout}
                   className="px-4 py-2 text-sm text-light-600 hover:text-light-900 transition-colors"
                 >
-                  Logout
+                  Déconnexion
                 </button>
               )}
             </div>

frontend/src/components/Navigation.tsx

@@ -28,7 +28,7 @@ export default function Navigation() {
             }`}
           >
             <Home className="w-5 h-5" />
-            <span className="font-medium">Dashboard</span>
+            <span className="font-medium">Tableau de bord</span>
           </Link>
 
           <Link
@@ -40,7 +40,7 @@ export default function Navigation() {
             }`}
           >
             <Compass className="w-5 h-5" />
-            <span className="font-medium">Discover</span>
+            <span className="font-medium">Découvrir</span>
           </Link>
         </div>
       </div>