Consolidate task logic into single source of truth (DRY refactor)

This refactor eliminates duplicate task logic across the codebase by
creating a centralized task package with three layers:

- predicates/: Pure Go functions defining task state logic (IsCompleted,
  IsOverdue, IsDueSoon, IsUpcoming, IsActive, IsInProgress, EffectiveDate)
- scopes/: GORM scope functions mirroring predicates for database queries
- categorization/: Chain of Responsibility pattern for kanban column assignment

Key fixes:
- Fixed PostgreSQL DATE vs TIMESTAMP comparison bug in scopes (added
  explicit ::timestamp casts) that caused summary/kanban count mismatches
- Fixed models/task.go IsOverdue() and IsDueSoon() to use EffectiveDate
  (NextDueDate ?? DueDate) instead of only DueDate
- Removed duplicate isTaskCompleted() helpers from task_repo.go and
  task_button_types.go

Files refactored to use consolidated logic:
- task_repo.go: Uses scopes for statistics, predicates for filtering
- task_button_types.go: Uses predicates instead of inline logic
- responses/task.go: Delegates to categorization package
- dashboard_handler.go: Uses scopes for task statistics
- residence_service.go: Uses predicates for report generation
- worker/jobs/handler.go: Documented SQL with predicate references

Added comprehensive tests:
- predicates_test.go: Unit tests for all predicate functions
- scopes_test.go: Integration tests verifying scopes match predicates
- consistency_test.go: Three-layer consistency tests ensuring predicates,
  scopes, and categorization all return identical results

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

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

internal/services/residence_service.go

@@ -11,6 +11,7 @@ import (
 	"github.com/treytartt/casera-api/internal/dto/responses"
 	"github.com/treytartt/casera-api/internal/models"
 	"github.com/treytartt/casera-api/internal/repositories"
+	"github.com/treytartt/casera-api/internal/task/predicates"
 )
 
 // Common errors
@@ -553,8 +554,9 @@ func (s *ResidenceService) GenerateTasksReport(residenceID, userID uint) (*Tasks
 	}
 
 	for i, task := range tasks {
-		// Determine if task is completed (has completions)
-		isCompleted := len(task.Completions) > 0
+		// Use predicates from internal/task/predicates as single source of truth
+		isCompleted := predicates.IsCompleted(&task)
+		isOverdue := predicates.IsOverdue(&task, now)
 
 		taskData := TaskReportData{
 			ID:          task.ID,
@@ -574,17 +576,19 @@ func (s *ResidenceService) GenerateTasksReport(residenceID, userID uint) (*Tasks
 		if task.Status != nil {
 			taskData.Status = task.Status.Name
 		}
-		if task.DueDate != nil {
-			taskData.DueDate = task.DueDate
+		// Use effective date for report (NextDueDate ?? DueDate)
+		effectiveDate := predicates.EffectiveDate(&task)
+		if effectiveDate != nil {
+			taskData.DueDate = effectiveDate
 		}
 
 		report.Tasks[i] = taskData
 
 		if isCompleted {
 			report.Completed++
-		} else if !task.IsCancelled && !task.IsArchived {
+		} else if predicates.IsActive(&task) {
 			report.Pending++
-			if task.DueDate != nil && task.DueDate.Before(now) {
+			if isOverdue {
 				report.Overdue++
 			}
 		}