feat: #2 G-force circle dashboard + .tsr export/import

- g_force dashboard: acceleration vector on 2G ring, lat/long G readout
- .tsr files export/import via API and UI
- Composite dashboard reverted (G-force is standalone)

server/api.py

@@ -469,3 +469,23 @@ async def api_start_playback(data: dict):
 async def api_stop_playback():
     _get_player().stop()
     return {"ok": True, "playing": False}
+
+
+@router.get("/recording/{filename}/export")
+async def api_export_recording(filename: str):
+    from fastapi.responses import FileResponse
+    from server.recorder import RECORDINGS_DIR
+    path = RECORDINGS_DIR / filename
+    if not path.exists():
+        raise HTTPException(404, "Recording not found")
+    return FileResponse(path, media_type="application/octet-stream", filename=filename)
+
+
+@router.post("/recording/import")
+async def api_import_recording(file: UploadFile = File(...)):
+    from server.recorder import RECORDINGS_DIR
+    if not file.filename or not file.filename.endswith('.tsr'):
+        raise HTTPException(400, "Only .tsr files are accepted")
+    dest = RECORDINGS_DIR / file.filename
+    dest.write_bytes(await file.read())
+    return {"ok": True}