Add onboarding email campaign system with post-verification welcome email

Implements automated onboarding emails to encourage user engagement:
- Post-verification welcome email with 5 tips (sent after email verification)
- "No Residence" email (2+ days after registration with no property)
- "No Tasks" email (5+ days after first residence with no tasks)

Key features:
- Each onboarding email type sent only once per user (enforced by unique constraint)
- Email open tracking via tracking pixel endpoint
- Daily scheduled job at 10:00 AM UTC to process eligible users
- Admin panel UI for viewing sent emails, stats, and manual sending
- Admin can send any email type to users from the user detail Testing section

New files:
- internal/models/onboarding_email.go - Database model with tracking
- internal/services/onboarding_email_service.go - Business logic and eligibility queries
- internal/handlers/tracking_handler.go - Email open tracking endpoint
- internal/admin/handlers/onboarding_handler.go - Admin API endpoints
- admin/src/app/(dashboard)/onboarding-emails/ - Admin UI pages

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

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

internal/router/router.go

@@ -68,6 +68,13 @@ func SetupRouter(deps *Dependencies) *gin.Engine {
 	// Health check endpoint (no auth required)
 	r.GET("/api/health/", healthCheck)
 
+	// Initialize onboarding email service for tracking handler
+	onboardingService := services.NewOnboardingEmailService(deps.DB, deps.EmailService, cfg.Server.BaseURL)
+
+	// Email tracking endpoint (no auth required - used by email tracking pixels)
+	trackingHandler := handlers.NewTrackingHandler(onboardingService)
+	r.GET("/api/track/open/:trackingID", trackingHandler.TrackEmailOpen)
+
 	// NOTE: Public static file serving removed for security.
 	// All uploaded media is now served through authenticated proxy endpoints:
 	// - GET /api/media/document/:id
@@ -132,8 +139,9 @@ func SetupRouter(deps *Dependencies) *gin.Engine {
 
 	// Set up admin routes (separate auth system)
 	adminDeps := &admin.Dependencies{
-		EmailService: deps.EmailService,
-		PushClient:   deps.PushClient,
+		EmailService:      deps.EmailService,
+		PushClient:        deps.PushClient,
+		OnboardingService: onboardingService,
 	}
 	admin.SetupRoutes(r, deps.DB, cfg, adminDeps)