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>

.claude/settings.local.json

@@ -6,7 +6,13 @@
       "Bash(git remote:*)",
       "Bash(git branch:*)",
       "Bash(git push:*)",
-      "Bash(ls -la /c/Claude/Podcastic/Dockerfile*)"
+      "Bash(ls -la /c/Claude/Podcastic/Dockerfile*)",
+      "Bash(npm run *)",
+      "WebFetch(domain:stitch.withgoogle.com)",
+      "Bash(npx tsc *)",
+      "Bash(git add *)",
+      "Bash(git pull *)",
+      "Bash(git stash *)"
     ]
   }
 }