chore: durcit la configuration pour la production

- mobile: externalise l'URL d'API via EXPO_PUBLIC_API_URL (repli localhost en dev)
- backend: .env.example adapté au projet (PostgreSQL, JWT, FRONTEND_URL, Redis)
- frontend/mobile: ajoute .env.example (+ exception gitignore front)
- mobile: supprime les 4 `any` (helper getApiError, type Feed, glyphMap Ionicons)
- backend: normalise le style PSR-12 via Pint (13 fichiers)

Tests backend 15/15, mobile tsc 0, Pint pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/Http/Controllers/Admin/AdminFeedController.php

@@ -39,7 +39,7 @@ class AdminFeedController extends Controller
         $feed = Feed::findOrFail($id);
         $data = $request->validated();
 
-        if (isset($data['titre']) && !isset($data['slug'])) {
+        if (isset($data['titre']) && ! isset($data['slug'])) {
             $data['slug'] = Str::slug($data['titre']);
         }