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/database/data_migrations.go

@@ -0,0 +1,94 @@
+package database
+
+import (
+	"sort"
+	"time"
+
+	"github.com/rs/zerolog/log"
+	"gorm.io/gorm"
+)
+
+// DataMigration tracks one-time data migrations that have been applied.
+type DataMigration struct {
+	ID        uint      `gorm:"primaryKey"`
+	Name      string    `gorm:"column:name;uniqueIndex;size:255;not null"`
+	AppliedAt time.Time `gorm:"column:applied_at;not null"`
+}
+
+func (DataMigration) TableName() string {
+	return "data_migrations"
+}
+
+// dataMigrationEntry pairs a name with its run function.
+type dataMigrationEntry struct {
+	Name string
+	Fn   func(tx *gorm.DB) error
+}
+
+// registry holds all registered one-time data migrations, in order.
+var registry []dataMigrationEntry
+
+// RegisterDataMigration adds a one-time migration. Call from init() functions.
+func RegisterDataMigration(name string, fn func(tx *gorm.DB) error) {
+	registry = append(registry, dataMigrationEntry{Name: name, Fn: fn})
+}
+
+// RunDataMigrations creates the tracking table and executes any migrations
+// that haven't been applied yet. Called once during server startup.
+func RunDataMigrations() error {
+	if db == nil {
+		return nil
+	}
+
+	// Ensure tracking table exists
+	if err := db.AutoMigrate(&DataMigration{}); err != nil {
+		return err
+	}
+
+	if len(registry) == 0 {
+		return nil
+	}
+
+	// Sort by name for deterministic order
+	sort.Slice(registry, func(i, j int) bool {
+		return registry[i].Name < registry[j].Name
+	})
+
+	// Load already-applied migrations
+	var applied []DataMigration
+	if err := db.Find(&applied).Error; err != nil {
+		return err
+	}
+	appliedSet := make(map[string]bool, len(applied))
+	for _, m := range applied {
+		appliedSet[m.Name] = true
+	}
+
+	// Run pending migrations
+	for _, entry := range registry {
+		if appliedSet[entry.Name] {
+			continue
+		}
+
+		log.Info().Str("migration", entry.Name).Msg("Running data migration")
+
+		err := db.Transaction(func(tx *gorm.DB) error {
+			if err := entry.Fn(tx); err != nil {
+				return err
+			}
+			// Record that this migration has been applied
+			return tx.Create(&DataMigration{
+				Name:      entry.Name,
+				AppliedAt: time.Now().UTC(),
+			}).Error
+		})
+		if err != nil {
+			log.Error().Err(err).Str("migration", entry.Name).Msg("Data migration failed")
+			return err
+		}
+
+		log.Info().Str("migration", entry.Name).Msg("Data migration completed")
+	}
+
+	return nil
+}