feat: add postcodes and outcodes tables for self-hosted lookup

database/migrations/2026_04_22_100000_create_postcodes_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::create('postcodes', function (Blueprint $table) {
+            $table->string('postcode', 7)->primary()->comment('Normalised: uppercase, no spaces');
+            $table->string('outcode', 4)->index();
+            $table->decimal('lat', 10, 7);
+            $table->decimal('lng', 10, 7);
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('postcodes');
+    }
+};

database/migrations/2026_04_22_100001_create_outcodes_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::create('outcodes', function (Blueprint $table) {
+            $table->string('outcode', 4)->primary();
+            $table->decimal('lat', 10, 7);
+            $table->decimal('lng', 10, 7);
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('outcodes');
+    }
+};