fix: phone uniqueness validation and DB constraint for users

- Replaced broken ->rules(fn (\$record)) with proper Filament ->unique()
  using ignoreRecord:true + modifyRuleUsing scoped to company_id,
  applied to both phone and email in MasterResource and UserResource
- Added migration 2026_09_26_000001 to add unique(company_id, phone)
  constraint on users table (nulls out duplicate phones before adding,
  MySQL allows multiple NULLs in unique index so blank phones are fine)
- Exception catch in Create/EditMaster and Create/EditUser now also
  handles UniqueConstraintViolationException on phone

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

database/migrations/2026_09_26_000001_add_phone_unique_to_users.php

@@ -0,0 +1,36 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        // Remove duplicate phones within the same company before adding constraint.
+        // Keep the oldest record (smallest id), null out the phone on duplicates.
+        DB::statement('
+            UPDATE users u1
+            JOIN users u2 ON u2.company_id = u1.company_id
+                         AND u2.phone = u1.phone
+                         AND u2.id < u1.id
+            SET u1.phone = NULL
+            WHERE u1.phone IS NOT NULL
+        ');
+
+        Schema::table('users', function (Blueprint $table) {
+            // MySQL/MariaDB allows multiple NULLs in a UNIQUE index,
+            // so users without a phone are unaffected.
+            $table->unique(['company_id', 'phone'], 'users_company_id_phone_unique');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('users', function (Blueprint $table) {
+            $table->dropUnique('users_company_id_phone_unique');
+        });
+    }
+};