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>

database/migrations/2026_07_18_000001_create_pagos_confirmados_table.php

@@ -0,0 +1,29 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::create('pagos_confirmados', function (Blueprint $table) {
+            $table->id();
+            $table->string('email_hash', 64)->unique();
+            $table->unsignedBigInteger('usuario_id')->nullable();
+            $table->integer('valor');
+            $table->string('canal', 20)->default('telegram');
+            $table->string('banco', 60)->nullable();
+            $table->string('referencia', 80)->nullable();
+            $table->timestamp('confirmado_en')->useCurrent();
+
+            $table->index('usuario_id');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('pagos_confirmados');
+    }
+};