feat(tui): folder jumps, open-all and a path filter in the browse popup

A browsed share only moved a row at a time, so a folder of a few
hundred files stood between the user and the next folder. J and K now
jump between folder rows, H and L close or open every folder, and /
filters the whole tree by path the way the results and the room list
filter: type to narrow, Enter keeps it, Esc clears it, then hides. A
folder under a filter shows the paths that match and d downloads just
those. The keys popup gains a browse section and the bar lists them.

soulseek-rs/src/models/mod.rs

@@ -8,9 +8,7 @@ pub use app_state::{
     AppState, ChatMessage, CommandBarMode, DownloadEntry, FocusedPane, LogView,
     MessageDirection, PaneLayout, SearchEntry, SearchStatus,
 };
-pub use browse::{
-    BrowseState, BrowseStatus, BrowseTabs, files_under, find_node,
-};
+pub use browse::{BrowseState, BrowseStatus, BrowseTabs};
 pub use file_display_data::FileDisplayData;
 pub use rooms::{RoomLine, RoomsState, RoomsView};
 pub use settings::{SettingsAction, SettingsMode, SettingsState};