Migrate from Gin to Echo framework and add comprehensive integration tests

Major changes:
- Migrate all handlers from Gin to Echo framework
- Add new apperrors, echohelpers, and validator packages
- Update middleware for Echo compatibility
- Add ArchivedHandler to task categorization chain (archived tasks go to cancelled_tasks column)
- Add 6 new integration tests:
  - RecurringTaskLifecycle: NextDueDate advancement for weekly/monthly tasks
  - MultiUserSharing: Complex sharing with user removal
  - TaskStateTransitions: All state transitions and kanban column changes
  - DateBoundaryEdgeCases: Threshold boundary testing
  - CascadeOperations: Residence deletion cascade effects
  - MultiUserOperations: Shared residence collaboration
- Add single-purpose repository functions for kanban columns (GetOverdueTasks, GetDueSoonTasks, etc.)
- Fix RemoveUser route param mismatch (userId -> user_id)
- Fix determineExpectedColumn helper to correctly prioritize in_progress over overdue

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

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

cmd/api/main.go

@@ -164,12 +164,12 @@ func main() {
 		StorageService:    storageService,
 		MonitoringService: monitoringService,
 	}
-	r := router.SetupRouter(deps)
+	e := router.SetupRouter(deps)
 
 	// Create HTTP server
 	srv := &http.Server{
 		Addr:         fmt.Sprintf(":%d", cfg.Server.Port),
-		Handler:      r,
+		Handler:      e,
 		ReadTimeout:  30 * time.Second,
 		WriteTimeout: 30 * time.Second,
 		IdleTimeout:  60 * time.Second,