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/upload.py

@@ -115,14 +115,21 @@ async def upload_garmin_export(
     extract_dir = dest_dir / f"garmin_{dest.stem}"
 
     task_ids = []
-    with zipfile.ZipFile(dest) as zf:
-        extracted = _safe_extract(zf, extract_dir)
+    try:
+        with zipfile.ZipFile(dest) as zf:
+            extracted = _safe_extract(zf, extract_dir)
+    except zipfile.BadZipFile:
+        dest.unlink(missing_ok=True)
+        raise HTTPException(status_code=400, detail="Uploaded file is not a valid ZIP archive")
 
+    has_health = False
     for path in extracted:
         suffix = path.suffix.lower()
         if suffix == ".fit":
             task = process_activity_file.delay(str(path), current_user.id, "fit")
             task_ids.append(task.id)
+        elif suffix == ".json":
+            has_health = True   # Garmin wellness data is exported as JSON files
         elif suffix == ".zip":
             # Garmin exports nest activity FIT files inside sub-zips
             # (e.g. DI-Connect-Uploaded-Files/UploadedFiles_*_Part*.zip)
@@ -137,6 +144,12 @@ async def upload_garmin_export(
                     task = process_activity_file.delay(str(np), current_user.id, "fit")
                     task_ids.append(task.id)
 
+    if not task_ids and not has_health:
+        raise HTTPException(
+            status_code=400,
+            detail="No fitness data found in this archive — make sure you uploaded your full Garmin Connect export ZIP",
+        )
+
     # Queue health/wellness data extraction
     health_task = process_garmin_health_zip.delay(str(dest), current_user.id)
 
@@ -163,8 +176,12 @@ async def upload_strava_export(
     extract_dir = dest_dir / f"strava_{dest.stem}"
 
     task_ids = []
-    with zipfile.ZipFile(dest) as zf:
-        extracted = _safe_extract(zf, extract_dir)
+    try:
+        with zipfile.ZipFile(dest) as zf:
+            extracted = _safe_extract(zf, extract_dir)
+    except zipfile.BadZipFile:
+        dest.unlink(missing_ok=True)
+        raise HTTPException(status_code=400, detail="Uploaded file is not a valid ZIP archive")
 
     for path in extracted:
         suffix = path.suffix.lower()
@@ -172,6 +189,12 @@ async def upload_strava_export(
             task = process_activity_file.delay(str(path), current_user.id, suffix[1:])
             task_ids.append(task.id)
 
+    if not task_ids:
+        raise HTTPException(
+            status_code=400,
+            detail="No activity files (.fit or .gpx) found in this Strava archive",
+        )
+
     return {
         "status": "queued",
         "activity_tasks": len(task_ids),