feat(tui): results across the top, with panes you can hide, zoom and Tab through

The results pane now has the whole width, where a long file name needs it,
and Searches, Downloads and Info share the row underneath. Tab and Shift-Tab
walk the panes, z zooms the focused one to the window, w hides it so the
others widen, and its number brings it back. Every list takes the same
navigation keys, the shortcuts bar wraps instead of cutting keys off, and ?
lists every key by pane, scrolling on a short terminal.

Follows up on #55.

soulseek-rs/src/models/mod.rs

@@ -6,7 +6,7 @@ mod settings;
 
 pub use app_state::{
     AppState, ChatMessage, CommandBarMode, DownloadEntry, FocusedPane,
-    MessageDirection, SearchEntry, SearchStatus,
+    MessageDirection, PaneLayout, SearchEntry, SearchStatus,
 };
 pub use browse::{
     BrowseState, BrowseStatus, BrowseTabs, files_under, find_node,