fix: correct stale doc comment on Profile's Interval phase fields

backend/internal/store/profile.go

@@ -27,12 +27,9 @@ type Profile struct {
 	Threshold60WarmupMinutes, Threshold60CooldownMinutes float64
 	MASTestWarmupMinutes, MASTestCooldownMinutes         float64
 
-	// IntervalWarmupMinutes/IntervalCooldownMinutes are not backed by
-	// dedicated columns: Interval phase detection uses the lap_intensity
-	// strategy (existing ACTIVE/REST lap tagging), not a fixed-duration
-	// guess. Kept here as a convenience zero-value for callers that don't
-	// yet distinguish strategies; always 0 until a future migration adds
-	// real columns if a fixed fallback is ever needed.
+	// IntervalWarmupMinutes/IntervalCooldownMinutes are persisted to dedicated
+	// columns (DEFAULT 0) but not yet used by phase-detection logic; reserved
+	// for future Interval fixed-duration strategy if needed.
 	IntervalWarmupMinutes, IntervalCooldownMinutes float64
 
 	CreatedAt, UpdatedAt string