fix: corregir pipeline de validación de pagos

- GeminiVisionService: eliminar thinkingConfig (rompe modelos flash),
  reducir maxOutputTokens 8192→512, timeout 20→40s, default gemini-2.0-flash
- PublicChat: detectar correctamente errores de Gemini (__error/__parse_error)
  que antes pasaban el guard if(!$datosPago) por ser arrays truthy
- PagoValidadorService: tolerancia de hora 0→3 min, remitente >=2→>=1 palabra
- CorreoImapService: break→continue en correos fuera de ventana (IMAP no
  garantiza orden cronológico), fetchSize *4→*2 para evitar timeout

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

app/Services/GeminiVisionService.php

@@ -15,7 +15,7 @@ class GeminiVisionService
     public function __construct()
     {
         $this->apiKey = ChatConfig::get('gemini_api_key', '');
-        $this->model  = ChatConfig::get('gemini_model', 'gemini-3.5-flash');
+        $this->model  = ChatConfig::get('gemini_model', 'gemini-2.0-flash');
     }
 
     public function extraerPago(string $base64, string $mimeType, ?int $usuarioId = null, string $canal = 'telegram'): ?array
@@ -36,8 +36,7 @@ class GeminiVisionService
             'contents'         => $contents,
             'generationConfig' => [
                 'temperature'     => 0.1,
-                'maxOutputTokens' => 8192,
-                'thinkingConfig'  => ['thinkingBudget' => 0],
+                'maxOutputTokens' => 512,
             ],
         ];
 
@@ -49,7 +48,7 @@ class GeminiVisionService
             $url = "https://generativelanguage.googleapis.com/{$ver}/models/{$this->model}:generateContent";
             try {
                 $resp = Http::withHeaders(['Content-Type' => 'application/json'])
-                    ->timeout(20)
+                    ->timeout(40)
                     ->post("{$url}?key={$this->apiKey}", $body);
 
                 if ($resp->successful()) {