feat(organisation): add contact fields to model and API

Add contact_name, contact_email, phone, website columns. Wire the new
fields through the Organisation model, update request validation,
response resource, and the TypeScript Organisation interface. Needed by
the upcoming dashboard + form-builder binding registry.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

api/database/migrations/2026_04_18_110000_add_contact_fields_to_organisations_table.php

@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+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('organisations', function (Blueprint $table) {
+            $table->string('contact_name')->nullable()->after('slug');
+            $table->string('contact_email')->nullable()->after('contact_name');
+            $table->string('phone')->nullable()->after('contact_email');
+            $table->string('website')->nullable()->after('phone');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('organisations', function (Blueprint $table) {
+            $table->dropColumn(['contact_name', 'contact_email', 'phone', 'website']);
+        });
+    }
+};