feat: funcionalidad de red social (feed, amigos, búsqueda)

- Migraciones: posts, post_likes, post_comments
- Modelos Post, PostLike, PostComment con relaciones
- User: métodos friendshipWith, isFriendWith, friendIds, posts
- PostController: feed, crear publicación con imagen, like toggle, comentarios, eliminar
- FriendshipController: listar solicitudes, enviar, aceptar, rechazar, toggle AJAX
- SocialProfileController: perfil público con publicaciones y estado de amistad
- UserSearchController: búsqueda AJAX por nombre con estado de amistad
- FriendRequestNotification: notificación al recibir solicitud
- Vistas: feed/index, feed/_post, friendships/index, social/profile
- Header: barra de búsqueda con autocomplete AJAX (agregar amigo / mensaje)
- Menú lateral: Comunidad, Amigos, Mensajes

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

app/Models/User.php

@@ -131,6 +131,45 @@ class User extends Authenticatable
         return $this->belongsToMany(Alumno::class);
     }
 
+    public function posts(): HasMany
+    {
+        return $this->hasMany(Post::class);
+    }
+
+    public function sentFriendRequests(): HasMany
+    {
+        return $this->hasMany(Friendship::class, 'sender_id');
+    }
+
+    public function receivedFriendRequests(): HasMany
+    {
+        return $this->hasMany(Friendship::class, 'receiver_id');
+    }
+
+    public function friendshipWith(User $user): ?Friendship
+    {
+        return Friendship::where(function ($q) use ($user) {
+                $q->where('sender_id', $this->id)->where('receiver_id', $user->id);
+            })
+            ->orWhere(function ($q) use ($user) {
+                $q->where('sender_id', $user->id)->where('receiver_id', $this->id);
+            })
+            ->first();
+    }
+
+    public function isFriendWith(User $user): bool
+    {
+        $friendship = $this->friendshipWith($user);
+        return $friendship?->status === 'accepted';
+    }
+
+    public function friendIds(): array
+    {
+        $sent     = Friendship::where('sender_id', $this->id)->where('status', 'accepted')->pluck('receiver_id');
+        $received = Friendship::where('receiver_id', $this->id)->where('status', 'accepted')->pluck('sender_id');
+        return $sent->merge($received)->unique()->values()->all();
+    }
+
     protected static function booted()
     {
         static::creating(function ($user) {