fix: tab layout, clear search state, and cleanup

UI: remove trackertable from the Search tab and reorder widgets to correct layout. Tab helper: add QLayout directly instead of wrapping it in a temporary QWidget to avoid extra nesting. Search helper: clear the trackertable rows and reset state.posts when starting a new search to ensure fresh results. Minor: import check_space in main and simplify an unused loop variable in libtorrent_int for clarity/linting.

src/network/libtorrent_int.py

@@ -23,7 +23,7 @@ def get_free_space_mb(dirname):
 
 def check_space():
     while not state.shutdown_event.is_set():
-        for magnet_uri, magnetdl in list(state.active_downloads.items()):
+        for _, magnetdl in list(state.active_downloads.items()):
             try:
                 status = magnetdl.status()
             except RuntimeError: