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/dto/responses/task.go

@@ -7,6 +7,7 @@ import (
 	"github.com/shopspring/decimal"
 
 	"github.com/treytartt/casera-api/internal/models"
+	"github.com/treytartt/casera-api/internal/task/categorization"
 )
 
 // TaskCategoryResponse represents a task category
@@ -365,53 +366,8 @@ func NewTaskCompletionWithTaskResponse(c *models.TaskCompletion, task *models.Ta
 }
 
 // DetermineKanbanColumn determines which kanban column a task belongs to.
-// This is a wrapper around the Chain of Responsibility implementation in
-// internal/task/categorization package. See that package for detailed
-// documentation on the categorization logic.
-//
-// Deprecated: Use categorization.DetermineKanbanColumn directly for new code.
+// Delegates to internal/task/categorization package which is the single source
+// of truth for task categorization logic.
 func DetermineKanbanColumn(task *models.Task, daysThreshold int) string {
-	// Import would cause circular dependency, so we replicate the logic here
-	// for backwards compatibility. The authoritative implementation is in
-	// internal/task/categorization/chain.go
-	if daysThreshold <= 0 {
-		daysThreshold = 30 // Default
-	}
-
-	now := time.Now().UTC()
-	threshold := now.AddDate(0, 0, daysThreshold)
-
-	// Priority order (Chain of Responsibility):
-	// 1. Cancelled (highest priority)
-	if task.IsCancelled {
-		return "cancelled_tasks"
-	}
-
-	// 2. Completed (one-time task with nil next_due_date and has completions)
-	if task.NextDueDate == nil && len(task.Completions) > 0 {
-		return "completed_tasks"
-	}
-
-	// 3. In Progress (status check)
-	if task.Status != nil && task.Status.Name == "In Progress" {
-		return "in_progress_tasks"
-	}
-
-	// 4. Overdue (next_due_date or due_date is in the past)
-	effectiveDate := task.NextDueDate
-	if effectiveDate == nil {
-		effectiveDate = task.DueDate
-	}
-	if effectiveDate != nil {
-		if effectiveDate.Before(now) {
-			return "overdue_tasks"
-		}
-		// 5. Due Soon (within threshold)
-		if effectiveDate.Before(threshold) {
-			return "due_soon_tasks"
-		}
-	}
-
-	// 6. Upcoming (default/fallback)
-	return "upcoming_tasks"
+	return categorization.DetermineKanbanColumn(task, daysThreshold)
 }