feat(tui): tabbed browsing — browse several users at once

Replace the single browse view with BrowseTabs (one tab per user),
mirroring the chat-room tabs. Browsing a new user (from search results
or a chat room's member list) opens or focuses their tab; Tab/Shift-Tab
switch between open users, 'w' closes the active tab, Esc hides the
popup while keeping the tabs. A tab bar shows the open users when more
than one is open, and each tab polls/loads independently. Re-browsing a
timed-out user retries. BrowseTabs is unit-tested.

soulseek-rs/src/ui/panes/browse_pane.rs

@@ -1,20 +1,62 @@
-use crate::models::{BrowseState, BrowseStatus};
+use crate::models::{BrowseState, BrowseStatus, BrowseTabs};
 use crate::ui::{
-    HIGHLIGHT_SYMBOL, border_style, border_type, error_style, format_bytes,
-    get_spinner_char, highlight_style, primary_style,
+    HIGHLIGHT_SYMBOL, border_style, border_type, dimmed_style, error_style,
+    format_bytes, get_spinner_char, highlight_style, primary_style,
 };
 use ratatui::{
     Frame,
-    layout::{Constraint, Rect},
-    text::Line,
+    layout::{Constraint, Layout, Rect},
+    style::Modifier,
+    text::{Line, Span},
     widgets::{
         Block, Borders, Cell, HighlightSpacing, Paragraph, Row, Table,
         TableState,
     },
 };
 
-/// Render the browse popup: a collapsible tree of a peer's shared files.
+/// Render the browse popup: a tab bar of browsed users (when more than one is
+/// open) above the active user's collapsible shared-file tree.
 pub fn render_browse_pane(
+    frame: &mut Frame,
+    area: Rect,
+    tabs: &BrowseTabs,
+    table_state: &mut TableState,
+    spinner_state: usize,
+) {
+    let Some(active) = tabs.active_tab() else {
+        return;
+    };
+
+    // With multiple users open, reserve the top row for a tab bar.
+    let tree_area = if tabs.tabs.len() > 1 {
+        let chunks =
+            Layout::vertical([Constraint::Length(1), Constraint::Fill(1)])
+                .split(area);
+        render_browse_tabs(frame, chunks[0], tabs);
+        chunks[1]
+    } else {
+        area
+    };
+
+    render_browse_one(frame, tree_area, active, table_state, spinner_state);
+}
+
+fn render_browse_tabs(frame: &mut Frame, area: Rect, tabs: &BrowseTabs) {
+    let mut spans: Vec<Span> = Vec::new();
+    for (i, tab) in tabs.tabs.iter().enumerate() {
+        let style = if i == tabs.active {
+            highlight_style().add_modifier(Modifier::BOLD)
+        } else {
+            dimmed_style()
+        };
+        spans.push(Span::styled(format!(" {} ", tab.username), style));
+        spans.push(Span::raw(" "));
+    }
+    frame.render_widget(Paragraph::new(Line::from(spans)), area);
+}
+
+/// Render one browsed user's shared-file tree.
+fn render_browse_one(
     frame: &mut Frame,
     area: Rect,
     browse: &BrowseState,
@@ -23,7 +65,7 @@ pub fn render_browse_pane(
 ) {
     let title = match browse.status {
         BrowseStatus::Loaded => format!(
-            " Browse {} — {} files, {} folders  (Enter/d: download, Esc: close) ",
+            " Browse {} — {} files, {} folders  (Enter/d: download, Tab: user, w: close, Esc: hide) ",
             browse.username, browse.file_count, browse.folder_count
         ),
         _ => format!(" Browse {} ", browse.username),