test: add Pest browser testing with SQLite :memory: schema

Set up end-to-end browser testing using Pest Browser Plugin + Playwright.
New v4 test suite uses SQLite :memory: database with pre-generated schema dump
(database/schema/testing-schema.sql) instead of running migrations, enabling
faster test startup.

- Add pestphp/pest-plugin-browser dependency
- Create GenerateTestingSchema command to export PostgreSQL schema to SQLite
- Add .env.testing configuration for isolated test environment
- Implement v4 test directory structure (Feature, Browser, Unit tests)
- Update Pest skill documentation with browser testing patterns, API reference,
  debugging techniques, and common pitfalls
- Configure phpunit.xml and tests/Pest.php for v4 suite
- Update package.json and docker-compose.dev.yml for testing dependencies

tests/v4/Feature/SqliteDatabaseTest.php

@@ -0,0 +1,18 @@
+<?php
+
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Schema;
+
+uses(RefreshDatabase::class);
+
+it('uses sqlite for testing', function () {
+    expect(DB::connection()->getDriverName())->toBe('sqlite');
+});
+
+it('runs migrations successfully', function () {
+    expect(Schema::hasTable('users'))->toBeTrue();
+    expect(Schema::hasTable('teams'))->toBeTrue();
+    expect(Schema::hasTable('servers'))->toBeTrue();
+    expect(Schema::hasTable('applications'))->toBeTrue();
+});