Initial commit: smartrun MVP

Garmin run classification and progression tracker. Go backend (MCP
client to mcp-garmin, SQLite store, deterministic rule engine, REST
API) and React/TS frontend (Dashboard, Review Queue, Workout Kinds).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/internal/store/syncstate.go

@@ -0,0 +1,37 @@
+package store
+
+import (
+	"context"
+	"fmt"
+)
+
+// SyncState tracks how far back into Garmin history a backfill has already
+// reached. Since activities are immutable once recorded, this lets a repeat
+// backfill skip everything already covered instead of re-fetching it.
+type SyncState struct {
+	EarliestSyncedDate *string // "YYYY-MM-DD", nil if backfill has never run
+	BackfillComplete   bool    // true once backfill has reached the configured horizon (or Garmin's own history start)
+}
+
+// GetSyncState returns the current backfill watermark (the singleton row,
+// created by migration 0002).
+func (db *DB) GetSyncState(ctx context.Context) (SyncState, error) {
+	var s SyncState
+	err := db.QueryRowContext(ctx, `SELECT earliest_synced_date, backfill_complete FROM sync_state WHERE id = 1`).
+		Scan(&s.EarliestSyncedDate, &s.BackfillComplete)
+	if err != nil {
+		return SyncState{}, fmt.Errorf("get sync state: %w", err)
+	}
+	return s, nil
+}
+
+// UpdateSyncState records progress of a backfill run.
+func (db *DB) UpdateSyncState(ctx context.Context, earliestSyncedDate string, complete bool) error {
+	_, err := db.ExecContext(ctx, `
+		UPDATE sync_state SET earliest_synced_date = ?, backfill_complete = ? WHERE id = 1`,
+		earliestSyncedDate, complete)
+	if err != nil {
+		return fmt.Errorf("update sync state: %w", err)
+	}
+	return nil
+}