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/dto/responses/residence.go

@@ -48,9 +48,10 @@ type ResidenceResponse struct {
 	PurchasePrice  *decimal.Decimal        `json:"purchase_price"`
 	IsPrimary      bool                    `json:"is_primary"`
 	IsActive       bool                    `json:"is_active"`
-	OverdueCount   int                     `json:"overdue_count"`
-	CreatedAt      time.Time               `json:"created_at"`
-	UpdatedAt      time.Time               `json:"updated_at"`
+	OverdueCount      int                `json:"overdue_count"`
+	CompletionSummary *CompletionSummary `json:"completion_summary,omitempty"`
+	CreatedAt         time.Time          `json:"created_at"`
+	UpdatedAt         time.Time          `json:"updated_at"`
 }
 
 // TotalSummary represents summary statistics for all residences
@@ -114,6 +115,28 @@ type SharePackageResponse struct {
 	ExpiresAt     *time.Time `json:"expires_at,omitempty"`
 }
 
+// ColumnCompletionCount represents completions from a specific kanban column
+type ColumnCompletionCount struct {
+	Column string `json:"column"`
+	Color  string `json:"color"`
+	Count  int    `json:"count"`
+}
+
+// MonthlyCompletionSummary represents completions for a single month
+type MonthlyCompletionSummary struct {
+	Month       string                 `json:"month"` // "2025-04" format
+	Completions []ColumnCompletionCount `json:"completions"`
+	Total       int                    `json:"total"`
+	Overflow    int                    `json:"overflow"` // completions beyond the display cap
+}
+
+// CompletionSummary represents task completion data for the honeycomb grid
+type CompletionSummary struct {
+	TotalAllTime      int                        `json:"total_all_time"`
+	TotalLast12Months int                        `json:"total_last_12_months"`
+	Months            []MonthlyCompletionSummary `json:"months"`
+}
+
 // === Factory Functions ===
 
 // NewResidenceUserResponse creates a ResidenceUserResponse from a User model