Feat: Agregada gestión de tablas ISR en settings

- Nueva tabla isr_tables y isr_brackets en BD
- Controlador IsrController para CRUD de tablas ISR
- Integración con pestaña ISR en settings
- Soporte para importación via CSV
- Captura manual de brackets

database/migrations/2024_01_01_000010_create_isr_tables_table.php

@@ -0,0 +1,28 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::create('isr_tables', function (Blueprint $table) {
+            $table->id();
+            $table->year('year')->unique();
+            $table->timestamps();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('isr_tables');
+    }
+};

database/migrations/2024_01_01_000011_create_isr_brackets_table.php

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+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::create('isr_brackets', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('isr_table_id')->constrained()->onDelete('cascade');
+            $table->decimal('lower_limit', 15, 2);
+            $table->decimal('upper_limit', 15, 2)->nullable()->comment('null significa "En adelante"');
+            $table->decimal('fixed_fee', 12, 2)->default(0);
+            $table->decimal('rate', 5, 2)->comment('porcentaje');
+            $table->unsignedInteger('order')->default(0);
+            $table->index('isr_table_id');
+            $table->index('order');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('isr_brackets');
+    }
+};

database/migrations/2026_04_21_000001_add_timestamps_to_isr_brackets_table.php

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+<?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::table('isr_brackets', function (Blueprint $table) {
+            $table->timestamps();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('isr_brackets', function (Blueprint $table) {
+            $table->dropTimestamps();
+        });
+    }
+};