Add honeycomb completion heatmap and data migration framework

- Add completion_summary endpoint data to residence detail response
- Track completed_from_column on task completions (overdue/due_soon/upcoming)
- Add GetCompletionSummary repo method with monthly aggregation
- Add one-time data migration framework (data_migrations table + registry)
- Add backfill migration to classify historical completions
- Add standalone backfill script for manual/dry-run usage

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/repositories/task_repo.go

@@ -8,6 +8,7 @@ import (
 	"github.com/rs/zerolog/log"
 	"gorm.io/gorm"
 
+	"github.com/treytartt/honeydue-api/internal/dto/responses"
 	"github.com/treytartt/honeydue-api/internal/models"
 	"github.com/treytartt/honeydue-api/internal/task"
 	"github.com/treytartt/honeydue-api/internal/task/categorization"
@@ -789,3 +790,125 @@ func (r *TaskRepository) GetOverdueCountByResidence(residenceIDs []uint, now tim
 
 	return countMap, nil
 }
+
+// kanbanColumnColors maps kanban column names to their hex colors.
+var kanbanColumnColors = map[string]string{
+	"overdue_tasks":     "#FF3B30",
+	"in_progress_tasks": "#5856D6",
+	"due_soon_tasks":    "#FF9500",
+	"upcoming_tasks":    "#007AFF",
+	"completed_tasks":   "#34C759",
+	"cancelled_tasks":   "#8E8E93",
+}
+
+// KanbanColumnColor returns the hex color for a kanban column name.
+func KanbanColumnColor(column string) string {
+	if color, ok := kanbanColumnColors[column]; ok {
+		return color
+	}
+	return "#34C759" // default to green
+}
+
+// completionAggRow is an internal type for scanning aggregated completion data.
+type completionAggRow struct {
+	ResidenceID         uint
+	CompletedFromColumn string
+	CompletedMonth      string
+	Count               int64
+}
+
+// GetCompletionSummary returns completion summary data for a single residence.
+// Returns total all-time count and monthly breakdowns (by column) for the last 12 months.
+func (r *TaskRepository) GetCompletionSummary(residenceID uint, now time.Time, maxPerMonth int) (*responses.CompletionSummary, error) {
+	// 1. Total all-time completions for this residence
+	var totalAllTime int64
+	err := r.db.Model(&models.TaskCompletion{}).
+		Joins("JOIN task_task ON task_task.id = task_taskcompletion.task_id").
+		Where("task_task.residence_id = ?", residenceID).
+		Count(&totalAllTime).Error
+	if err != nil {
+		return nil, err
+	}
+
+	// 2. Monthly breakdown for last 12 months
+	startDate := time.Date(now.Year()-1, now.Month(), 1, 0, 0, 0, 0, now.Location())
+
+	// Use dialect-appropriate date formatting (PostgreSQL vs SQLite)
+	dateExpr := "TO_CHAR(task_taskcompletion.completed_at, 'YYYY-MM')"
+	if r.db.Dialector.Name() == "sqlite" {
+		dateExpr = "strftime('%Y-%m', task_taskcompletion.completed_at)"
+	}
+
+	var rows []completionAggRow
+	err = r.db.Model(&models.TaskCompletion{}).
+		Select(fmt.Sprintf("task_task.residence_id, task_taskcompletion.completed_from_column, %s as completed_month, COUNT(*) as count", dateExpr)).
+		Joins("JOIN task_task ON task_task.id = task_taskcompletion.task_id").
+		Where("task_task.residence_id = ? AND task_taskcompletion.completed_at >= ?", residenceID, startDate).
+		Group(fmt.Sprintf("task_task.residence_id, task_taskcompletion.completed_from_column, %s", dateExpr)).
+		Order("completed_month ASC").
+		Scan(&rows).Error
+	if err != nil {
+		return nil, err
+	}
+
+	// Build month map
+	type monthData struct {
+		columns map[string]int
+		total   int
+	}
+	monthMap := make(map[string]*monthData)
+
+	// Initialize all 12 months
+	for i := 0; i < 12; i++ {
+		m := startDate.AddDate(0, i, 0)
+		key := m.Format("2006-01")
+		monthMap[key] = &monthData{columns: make(map[string]int)}
+	}
+
+	// Populate from query results
+	totalLast12 := 0
+	for _, row := range rows {
+		md, ok := monthMap[row.CompletedMonth]
+		if !ok {
+			continue
+		}
+		md.columns[row.CompletedFromColumn] = int(row.Count)
+		md.total += int(row.Count)
+		totalLast12 += int(row.Count)
+	}
+
+	// Convert to response DTOs
+	months := make([]responses.MonthlyCompletionSummary, 0, 12)
+	for i := 0; i < 12; i++ {
+		m := startDate.AddDate(0, i, 0)
+		key := m.Format("2006-01")
+		md := monthMap[key]
+
+		completions := make([]responses.ColumnCompletionCount, 0)
+		for col, count := range md.columns {
+			completions = append(completions, responses.ColumnCompletionCount{
+				Column: col,
+				Color:  KanbanColumnColor(col),
+				Count:  count,
+			})
+		}
+
+		overflow := 0
+		if md.total > maxPerMonth {
+			overflow = md.total - maxPerMonth
+		}
+
+		months = append(months, responses.MonthlyCompletionSummary{
+			Month:       key,
+			Completions: completions,
+			Total:       md.total,
+			Overflow:    overflow,
+		})
+	}
+
+	return &responses.CompletionSummary{
+		TotalAllTime:      int(totalAllTime),
+		TotalLast12Months: totalLast12,
+		Months:            months,
+	}, nil
+}