Migrate dev server from MongoDB to SQLite

- Replace mongooseAdapter with sqliteAdapter in payload config
- Update database configuration to use file:./dev.db
- Remove MongoDB memory database helper and references
- Simplify start script by removing verbose logging and MongoDB messaging
- Fix email processing with immediate send support and proper queue handling
- Restructure app with route groups for frontend/admin separation
- Add dashboard and test pages for email management
- Update API routes for improved email processing and testing

🤖 Generated with [Claude Code](https://claude.ai/code)

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

dev/start-dev.js

@@ -3,26 +3,14 @@
 // Development startup script for PayloadCMS Mailing Plugin
 // This ensures proper environment setup and provides helpful information
 
-console.log('🚀 PayloadCMS Mailing Plugin - Development Mode')
-console.log('=' .repeat(50))
-
 // Set development environment
 process.env.NODE_ENV = process.env.NODE_ENV || 'development'
 
-// Enable in-memory MongoDB by default for development
+// Set default SQLite database for development
 if (!process.env.DATABASE_URI) {
-  process.env.USE_MEMORY_DB = 'true'
-  console.log('📦 Using in-memory MongoDB (no installation required)')
-} else {
-  console.log(`🔗 Using external MongoDB: ${process.env.DATABASE_URI}`)
+  process.env.DATABASE_URI = 'file:./dev.db'
 }
 
-console.log('')
-console.log('🔧 Starting development server...')
-console.log('📧 Mailing plugin configured with test transport')
-console.log('🎯 Test interface will be available at: /mailing-test')
-console.log('')
-
 // Import and start Next.js
 import('next/dist/cli/next-dev.js')
   .then(({ nextDev }) => {
@@ -35,11 +23,9 @@ import('next/dist/cli/next-dev.js')
 
 // Handle graceful shutdown
 process.on('SIGTERM', () => {
-  console.log('\n🛑 Shutting down development server...')
   process.exit(0)
 })
 
 process.on('SIGINT', () => {
-  console.log('\n🛑 Shutting down development server...')
   process.exit(0)
 })