feat(api): reshape /api/sync/status for phase-aware progress

Replaces detail_fill_progress ({Done, Total}) with progress ({Phase,
Done, Total}), and adds workouts_pending (mirroring
activities_pending_details) from the new CountActivitiesMissingWorkout.
Frontend types updated to match -- GarminConnection.tsx is intentionally
left broken by this commit alone; it's fixed in the next commit that
adds SyncModal.

backend/internal/api/sync.go

@@ -73,7 +73,12 @@ func (s *Server) handleSyncStatus(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusInternalServerError, err.Error())
 		return
 	}
-	remaining, err := s.DB.CountActivitiesMissingDetails(r.Context(), userID)
+	pendingDetails, err := s.DB.CountActivitiesMissingDetails(r.Context(), userID)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+	pendingWorkouts, err := s.DB.CountActivitiesMissingWorkout(r.Context(), userID)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, err.Error())
 		return
@@ -92,8 +97,9 @@ func (s *Server) handleSyncStatus(w http.ResponseWriter, r *http.Request) {
 
 	resp := map[string]any{
 		"in_progress":                inProgress,
-		"detail_fill_progress":       progress,
-		"activities_pending_details": remaining,
+		"progress":                   progress,
+		"activities_pending_details": pendingDetails,
+		"workouts_pending":           pendingWorkouts,
 	}
 	if ok {
 		resp["last_run"] = run