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.

frontend/src/types/api.ts

@@ -173,7 +173,7 @@ export interface ProgressionPoint {
 
 export interface SyncRun {
   ID: number;
-  Kind: "backfill" | "incremental";
+  Kind: "backfill" | "incremental" | "full";
   StartedAt: string;
   FinishedAt: string | null;
   ActivitiesFetched: number;
@@ -194,15 +194,17 @@ export interface SessionInfo {
   garmin_connected: boolean;
 }
 
-export interface DetailFillProgress {
+export interface SyncProgress {
+  Phase: "idle" | "discovering" | "activities" | "workouts";
   Done: number;
   Total: number;
 }
 
 export interface SyncStatus {
   in_progress: boolean;
-  detail_fill_progress: DetailFillProgress;
+  progress: SyncProgress;
   activities_pending_details: number;
+  workouts_pending: number;
   last_run?: SyncRun;
 }