feat(tui): browse or PM a user from a chat room's member list

The member list in an open room is now selectable with the arrow keys.
Press 'b' to browse the highlighted user's shared files (opens the
browse tree) or 'm' to send them a private message (opens the compose
bar pre-filled with the recipient). Selection resets when switching
rooms; RoomsState navigation is unit-tested.

soulseek-rs/src/models/rooms.rs

@@ -69,6 +69,8 @@ pub struct RoomsState {
     pub view: RoomsView,
     /// Whether the compose input for the active room is capturing keys.
     pub composing: bool,
+    /// Selected index into the active room's member list (for browse/PM).
+    pub user_selected: usize,
 }
 
 impl Default for RoomsState {
@@ -89,6 +91,7 @@ impl RoomsState {
             active: 0,
             view: RoomsView::List,
             composing: false,
+            user_selected: 0,
         }
     }
 
@@ -133,6 +136,7 @@ impl RoomsState {
     /// `true` if the room was newly opened (so the caller should `join_room`).
     pub fn focus_or_open(&mut self, name: &str) -> bool {
         self.view = RoomsView::Chat;
+        self.user_selected = 0;
         if let Some(idx) = self.open_index(name) {
             self.active = idx;
             self.mark_active_read();
@@ -144,6 +148,26 @@ impl RoomsState {
         }
     }
 
+    /// The username highlighted in the active room's member list, if any.
+    #[must_use]
+    pub fn selected_user(&self) -> Option<String> {
+        self.active_room()
+            .and_then(|r| r.users.get(self.user_selected).cloned())
+    }
+
+    pub const fn select_user_up(&mut self) {
+        self.user_selected = self.user_selected.saturating_sub(1);
+    }
+
+    pub fn select_user_down(&mut self) {
+        if let Some(room) = self.active_room()
+            && !room.users.is_empty()
+        {
+            self.user_selected =
+                (self.user_selected + 1).min(room.users.len() - 1);
+        }
+    }
+
     /// Close the active tab, returning its room name (for `leave_room`).
     pub fn close_active(&mut self) -> Option<String> {
         if self.active >= self.open.len() {
@@ -153,6 +177,7 @@ impl RoomsState {
         if self.active >= self.open.len() {
             self.active = self.open.len().saturating_sub(1);
         }
+        self.user_selected = 0;
         if self.open.is_empty() {
             self.view = RoomsView::List;
         } else {
@@ -165,6 +190,7 @@ impl RoomsState {
     pub fn next_tab(&mut self) {
         if !self.open.is_empty() {
             self.active = (self.active + 1) % self.open.len();
+            self.user_selected = 0;
             self.mark_active_read();
         }
     }
@@ -172,6 +198,7 @@ impl RoomsState {
     pub fn prev_tab(&mut self) {
         if !self.open.is_empty() {
             self.active = (self.active + self.open.len() - 1) % self.open.len();
+            self.user_selected = 0;
             self.mark_active_read();
         }
     }
@@ -469,6 +496,36 @@ mod tests {
         assert_eq!(state.total_unread(), 0);
     }
 
+    #[test]
+    fn user_selection_navigates_and_resets_across_tabs() {
+        let mut state = RoomsState::new();
+        state.apply_event(
+            RoomEvent::Joined {
+                room: "jazz".to_string(),
+                users: vec![
+                    "alice".to_string(),
+                    "bob".to_string(),
+                    "carol".to_string(),
+                ],
+            },
+            None,
+        );
+        state.focus_or_open("jazz");
+        assert_eq!(state.selected_user().as_deref(), Some("alice"));
+        state.select_user_down();
+        state.select_user_down();
+        assert_eq!(state.selected_user().as_deref(), Some("carol"));
+        state.select_user_down(); // clamps at the last user
+        assert_eq!(state.selected_user().as_deref(), Some("carol"));
+        state.select_user_up();
+        assert_eq!(state.selected_user().as_deref(), Some("bob"));
+
+        // Opening another room resets the user highlight.
+        state.focus_or_open("blues");
+        assert_eq!(state.user_selected, 0);
+        assert_eq!(state.selected_user(), None); // blues has no members yet
+    }
+
     #[test]
     fn user_joined_and_left_update_membership() {
         let mut state = RoomsState::new();