Set up database seeding architecture and E2E testing infrastructure

- Add CLAUDE.md: AI assistant instructions for MetaBuilder project architecture
- Add TESTING.md: Comprehensive E2E testing guide and troubleshooting

Core changes:
- Create Playwright global.setup.ts to seed database before E2E tests
- Add /api/setup endpoint to trigger database seeding via HTTP
- Implement seed-home-page.ts module loaded from ui_home package metadata
- Create ui_home/seed/metadata.json defining home page PageConfig seed data

Architecture established:
- Packages define seed data in seed/metadata.json
- Seed functions are idempotent (check before creating)
- Global setup calls /api/setup before running tests
- Database schema must be created via 'npm run db:push' before seeding

Test flow:
1. Playwright starts webServer (generates Prisma client, starts Next.js)
2. Global setup waits for server, calls POST /api/setup
3. Seeding creates default data from packages
4. E2E tests run against seeded database

This establishes proper separation of concerns:
- DBAL adapter for database access (not raw Prisma)
- Package-driven seed data (not hardcoded in code)
- HTTP endpoint for explicit database initialization
- Idempotent seeds (safe to rerun)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

packages/ui_home/seed/metadata.json

@@ -0,0 +1,23 @@
+{
+  "packageId": "ui_home",
+  "name": "Home Page",
+  "version": "1.0.0",
+  "description": "Seed data for ui_home package - defines the home page",
+  "author": "MetaBuilder Team",
+  "category": "ui",
+  "exports": {
+    "components": [],
+    "pages": [
+      {
+        "path": "/",
+        "title": "MetaBuilder",
+        "description": "Data-driven application platform",
+        "component": "home_page",
+        "level": 0,
+        "requiresAuth": false,
+        "isPublished": true
+      }
+    ]
+  },
+  "dependencies": []
+}