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/worker/jobs/handler.go

@@ -101,16 +101,16 @@ func (h *Handler) HandleTaskReminder(ctx context.Context, task *asynq.Task) erro
 	log.Info().Int("eligible_users", len(eligibleUserIDs)).Msg("Found users eligible for task reminders this hour")
 
 	// Step 2: Query tasks due today or tomorrow only for eligible users
-	// A task is considered "completed" (and should be excluded) if:
-	// - NextDueDate IS NULL AND it has at least one completion record
-	// This matches the kanban categorization logic
+	// Completion detection logic matches internal/task/predicates.IsCompleted:
+	// A task is "completed" when NextDueDate == nil AND has at least one completion.
+	// See internal/task/scopes.ScopeNotCompleted for the SQL equivalent.
 	var dueSoonTasks []models.Task
 	err = h.db.Preload("Status").Preload("Completions").Preload("Residence").
 		Where("(due_date >= ? AND due_date < ?) OR (next_due_date >= ? AND next_due_date < ?)",
 			today, dayAfterTomorrow, today, dayAfterTomorrow).
 		Where("is_cancelled = false").
 		Where("is_archived = false").
-		// Exclude completed tasks: tasks with no next_due_date AND at least one completion
+		// Exclude completed tasks (matches scopes.ScopeNotCompleted)
 		Where("NOT (next_due_date IS NULL AND EXISTS (SELECT 1 FROM task_taskcompletion tc WHERE tc.task_id = task_task.id))").
 		Where("(assigned_to_id IN ? OR residence_id IN (SELECT id FROM residence_residence WHERE owner_id IN ?))",
 			eligibleUserIDs, eligibleUserIDs).
@@ -218,15 +218,15 @@ func (h *Handler) HandleOverdueReminder(ctx context.Context, task *asynq.Task) e
 	log.Info().Int("eligible_users", len(eligibleUserIDs)).Msg("Found users eligible for overdue reminders this hour")
 
 	// Step 2: Query overdue tasks only for eligible users
-	// A task is considered "completed" (and should be excluded) if:
-	// - NextDueDate IS NULL AND it has at least one completion record
-	// This matches the kanban categorization logic
+	// Completion detection logic matches internal/task/predicates.IsCompleted:
+	// A task is "completed" when NextDueDate == nil AND has at least one completion.
+	// See internal/task/scopes.ScopeNotCompleted for the SQL equivalent.
 	var overdueTasks []models.Task
 	err = h.db.Preload("Status").Preload("Completions").Preload("Residence").
 		Where("due_date < ? OR next_due_date < ?", today, today).
 		Where("is_cancelled = false").
 		Where("is_archived = false").
-		// Exclude completed tasks: tasks with no next_due_date AND at least one completion
+		// Exclude completed tasks (matches scopes.ScopeNotCompleted)
 		Where("NOT (next_due_date IS NULL AND EXISTS (SELECT 1 FROM task_taskcompletion tc WHERE tc.task_id = task_task.id))").
 		Where("(assigned_to_id IN ? OR residence_id IN (SELECT id FROM residence_residence WHERE owner_id IN ?))",
 			eligibleUserIDs, eligibleUserIDs).
@@ -299,6 +299,9 @@ func (h *Handler) HandleDailyDigest(ctx context.Context, task *asynq.Task) error
 	nextWeek := today.AddDate(0, 0, 7)
 
 	// Get all users with their task statistics
+	// Completion detection logic matches internal/task/predicates.IsCompleted:
+	// A task is "completed" when NextDueDate == nil AND has at least one completion.
+	// We use COALESCE(next_due_date, due_date) as the effective date for categorization.
 	var userStats []struct {
 		UserID       uint
 		TotalTasks   int
@@ -310,8 +313,16 @@ func (h *Handler) HandleDailyDigest(ctx context.Context, task *asynq.Task) error
 		SELECT
 			u.id as user_id,
 			COUNT(DISTINCT t.id) as total_tasks,
-			COUNT(DISTINCT CASE WHEN t.due_date < ? AND tc.id IS NULL THEN t.id END) as overdue_tasks,
-			COUNT(DISTINCT CASE WHEN t.due_date >= ? AND t.due_date < ? AND tc.id IS NULL THEN t.id END) as due_this_week
+			COUNT(DISTINCT CASE
+				WHEN COALESCE(t.next_due_date, t.due_date) < ?
+				AND NOT (t.next_due_date IS NULL AND EXISTS (SELECT 1 FROM task_taskcompletion tc WHERE tc.task_id = t.id))
+				THEN t.id
+			END) as overdue_tasks,
+			COUNT(DISTINCT CASE
+				WHEN COALESCE(t.next_due_date, t.due_date) >= ? AND COALESCE(t.next_due_date, t.due_date) < ?
+				AND NOT (t.next_due_date IS NULL AND EXISTS (SELECT 1 FROM task_taskcompletion tc WHERE tc.task_id = t.id))
+				THEN t.id
+			END) as due_this_week
 		FROM auth_user u
 		JOIN residence_residence r ON r.owner_id = u.id OR r.id IN (
 			SELECT residence_id FROM residence_residence_users WHERE user_id = u.id
@@ -319,7 +330,6 @@ func (h *Handler) HandleDailyDigest(ctx context.Context, task *asynq.Task) error
 		JOIN task_task t ON t.residence_id = r.id
 			AND t.is_cancelled = false
 			AND t.is_archived = false
-		LEFT JOIN task_taskcompletion tc ON t.id = tc.task_id
 		WHERE u.is_active = true
 		GROUP BY u.id
 		HAVING COUNT(DISTINCT t.id) > 0