Prevent double-confirmation of same payment by different users

- Create pagos_confirmados table to track consumed email receipts
- PagoValidadorService now validates: valor + fecha + hora (±10min) + llave Bancolombia
- Each matched email is hashed (sha1 body+date) and marked as used; a second
  match returns estado=ya_usado instead of confirmado
- Add partial remitente name matching against the registered user's name
- GeminiVisionService prompt now extracts llave (@xxx) from the receipt image
- TelegramBotService shows distinct message for ya_usado state

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

app/Models/PagoConfirmado.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+
+class PagoConfirmado extends Model
+{
+    public $timestamps = false;
+
+    protected $fillable = [
+        'email_hash',
+        'usuario_id',
+        'valor',
+        'canal',
+        'banco',
+        'referencia',
+        'confirmado_en',
+    ];
+
+    protected $casts = [
+        'confirmado_en' => 'datetime',
+    ];
+
+    public static function yaUsado(string $hash): bool
+    {
+        return static::where('email_hash', $hash)->exists();
+    }
+
+    public static function marcar(string $hash, array $datos): void
+    {
+        static::create(array_merge(['email_hash' => $hash], $datos));
+    }
+}