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/ui/panes/browse_pane.rs

@@ -62,8 +62,20 @@ fn render_browse_one(
     spinner_state: usize,
 ) {
     let title = match browse.status {
+        BrowseStatus::Loaded
+            if browse.filtering || !browse.filter().is_empty() =>
+        {
+            format!(
+                " Browse {} — {} files, {} folders · filter: {}{}  (Enter: keep, Esc: clear) ",
+                browse.username,
+                browse.file_count,
+                browse.folder_count,
+                browse.filter(),
+                if browse.filtering { "_" } else { "" }
+            )
+        }
         BrowseStatus::Loaded => format!(
-            " Browse {} — {} files, {} folders  (Enter/d: download, Tab: user, w: close, Esc: hide) ",
+            " Browse {} — {} files, {} folders  (Enter/d: download, /: filter, Tab: user, w: close, Esc: hide) ",
             browse.username, browse.file_count, browse.folder_count
         ),
         _ => format!(" Browse {} ", browse.username),
@@ -105,6 +117,15 @@ fn render_browse_one(
             ];
             frame.render_widget(Paragraph::new(text).block(block), area);
         }
+        BrowseStatus::Loaded
+            if browse.rows().is_empty() && !browse.filter().is_empty() =>
+        {
+            let text = format!("Nothing here matches '{}'.", browse.filter());
+            frame.render_widget(
+                Paragraph::new(text).style(dimmed_style()).block(block),
+                area,
+            );
+        }
         BrowseStatus::Loaded => {
             let all = browse.rows();
             let window = visible_range(