Add trend-range gating, vehicle filter, sync cancel, moving time, and UI fixes

- Grey out trend ranges beyond available health history
- Reject implausibly fast (vehicle) activities on upload with feedback
- Add cancel button + cooperative cancellation for Garmin sync
- Show daily steps prominently on the dashboard
- Clear errors for malformed/empty upload ZIPs
- Snap-target dot when drawing a segment on the map
- Time-axis fallback for stationary/HIIT HR timelines; hide map when no GPS
- Parse and display moving time (timer) vs elapsed; backfill task
- Restyle SegmentsPanel like RouteLeaderboard; Laps/Routes/Segments on one row

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/app/api/garmin_sync.py

@@ -13,6 +13,19 @@ from app.models.user import User, GarminConnectConfig
 router = APIRouter()
 
 
+def _redis_client():
+    import redis as redis_lib
+    return redis_lib.Redis.from_url(settings.redis_url)
+
+
+def sync_task_key(user_id: int) -> str:
+    return f"garmin_sync_task:{user_id}"
+
+
+def sync_cancel_key(user_id: int) -> str:
+    return f"garmin_sync_cancel:{user_id}"
+
+
 class GarminConfigIn(BaseModel):
     email: str
     password: Optional[str] = None       # plaintext; encrypted before storage. None = keep existing.
@@ -183,4 +196,47 @@ async def trigger_sync(
 
     from app.workers.tasks import sync_garmin_connect_user
     task = sync_garmin_connect_user.delay(current_user.id)
+
+    # Track the active task id and clear any stale cancel flag so the new sync runs.
+    try:
+        r = _redis_client()
+        r.delete(sync_cancel_key(current_user.id))
+        r.set(sync_task_key(current_user.id), task.id, ex=3600)
+    except Exception:
+        pass
+
     return {"task_id": task.id, "status": "queued"}
+
+
+@router.post("/cancel")
+async def cancel_sync(
+    current_user: User = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """Request cancellation of the user's in-progress Garmin sync. The running task
+    checks this flag between items and aborts cooperatively."""
+    from app.workers.tasks import celery_app
+
+    try:
+        r = _redis_client()
+        r.set(sync_cancel_key(current_user.id), "1", ex=3600)
+        task_id = r.get(sync_task_key(current_user.id))
+        if task_id:
+            tid = task_id.decode() if isinstance(task_id, (bytes, bytearray)) else task_id
+            # terminate=False: don't kill a running worker mid-transaction; the
+            # cooperative flag handles an already-running task, and this revoke
+            # prevents a still-queued one from starting.
+            celery_app.control.revoke(tid, terminate=False)
+    except Exception:
+        pass
+
+    # Reflect intent immediately so the UI updates before the worker writes "Cancelled".
+    result = await db.execute(
+        select(GarminConnectConfig).where(GarminConnectConfig.user_id == current_user.id)
+    )
+    cfg = result.scalar_one_or_none()
+    if cfg:
+        cfg.last_sync_status = "Cancelling…"
+        await db.commit()
+
+    return {"status": "cancelling"}