feat: implement email case-insensitive queries (fix #318)

database/migrations/2026_03_28_050000_lowercase_existing_emails.php

@@ -0,0 +1,38 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Log;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        // 统计需要转换的记录数
+        $count = DB::table('v2_user')
+            ->whereNotNull('email')
+            ->whereRaw('email != LOWER(email)')
+            ->count();
+
+        if ($count > 0) {
+            Log::info("Converting {$count} email(s) to lowercase");
+            DB::table('v2_user')
+                ->whereNotNull('email')
+                ->whereRaw('email != LOWER(email)')
+                ->update(['email' => DB::raw('LOWER(email)')]);
+                
+            Log::info("Email lowercase conversion completed");
+        }
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        // 无法恢复原始大小写
+    }
+};