segments: clear stored efforts before rescan so stale entries are removed

Both trigger_detect and me_segment_rescan were appending-only, so false
efforts recorded before the geometric speed check fix remained after
rescan. Now each rescan path clears the effort file first, making the
result authoritative.

bincio/serve/server.py

@@ -2588,6 +2588,7 @@ async def trigger_detect(
     dd = _get_data_dir()
     if _seg_store.load_segment(dd, segment_id) is None:
         raise HTTPException(404, "Segment not found")
+    _seg_store.save_efforts(dd, user.handle, segment_id, [])
     total = _scan_segment_for_user(dd, user.handle, segment_id)
     return JSONResponse({"ok": True, "efforts_found": total})
 
@@ -2610,6 +2611,9 @@ async def me_segment_rescan(
     if not segments:
         return JSONResponse({"ok": True, "efforts_found": 0})
 
+    for seg in segments:
+        _seg_store.save_efforts(dd, user.handle, seg.id, [])
+
     total = 0
     for detail_path in sorted(acts_dir.glob("*.json")):
         if ".timeseries." in detail_path.name: