fix(friends): self-heal presence + add manual Rescan button

The friends list only ever updated a friend's status on a *successful*
presence probe, so it could ratchet a status up (offline -> online -> in a
room) but never down. A friend who dropped, left a room, or went invisible
kept showing a stale "online"/"in a room" status until PeerSpeak was
relaunched (which cleared the in-memory presence map back to offline).

The 60s auto-refresh scheduler already existed; the bug was that
`probe_friends_once` emitted nothing on a failed probe. Now every pass
reports a *definitive* status for every friend: a failed probe (or a
friend with no known address) is mapped to a new `FriendPresence::Offline`
via the pure, tested `presence::presence_from_probe`, so the list
self-heals each cycle.

Also adds a manual "⟳ Rescan" button to the Friends panel (new
`CoreCommand::RefreshFriends` -> immediate probe pass) for instant
feedback instead of waiting up to 60s.

469 lib tests pass, clippy clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/mod.rs

@@ -366,6 +366,9 @@ pub enum AppMessage {
     AddFriendFromRoom(EndpointId),
     RemoveFriend(EndpointId),
     RenameFriend(EndpointId, String),
+    /// Manually rescan all friends' presence now (the ⟳ button), instead of waiting
+    /// for the 60s scheduler tick. Statuses update as the probe replies arrive.
+    RefreshFriends,
     /// Join the gathering a friend is in (W7 B2), via the member ticket their
     /// presence reply carried. Mirrors a manual ticket join.
     JoinFriendRoom(String),
@@ -1894,6 +1897,11 @@ fn update(state: &mut AppState, message: AppMessage) -> Task<AppMessage> {
                 let _ = state.controller.send(CoreCommand::RenameFriend(id, new_name));
             }
         }
+        AppMessage::RefreshFriends => {
+            // Kick an immediate presence pass; the list updates as replies land.
+            let _ = state.controller.send(CoreCommand::RefreshFriends);
+            state.status_message = "Rescanning friends…".to_string();
+        }
         AppMessage::JoinFriendRoom(ticket) => {
             // Join via the friend's member ticket (same path as a manual join).
             let input_device = state.selected_input.as_ref().map(|d| d.name.clone());
@@ -3684,7 +3692,11 @@ fn friends_panel(state: &AppState) -> Element<'_, AppMessage> {
                 Some(crate::presence::FriendPresence::Online) => {
                     text("● online").size(11).color(color_green).into()
                 }
-                None => text("○ offline").size(11).color(color_subtext).into(),
+                // An explicit Offline (probe failed / no address) and a missing
+                // entry (not yet probed) both render as offline.
+                Some(crate::presence::FriendPresence::Offline) | None => {
+                    text("○ offline").size(11).color(color_subtext).into()
+                }
             };
             friend_rows = friend_rows.push(
                 row![
@@ -3768,10 +3780,27 @@ fn friends_panel(state: &AppState) -> Element<'_, AppMessage> {
     } else {
         column![].into()
     };
+    // Header: title + a manual "Rescan" button. Presence is also auto-refreshed
+    // every 60s, but the button forces an immediate pass for instant feedback.
+    // Only shown when there are friends to scan.
+    let title_row: Element<'_, AppMessage> = if has_friends {
+        row![
+            text("FRIENDS").size(18).color(color_text),
+            horizontal_space(),
+            button(text("⟳ Rescan").size(12))
+                .on_press(AppMessage::RefreshFriends)
+                .style(b_style(color_surface, color_blue, color_text, 6.0))
+                .padding(6),
+        ]
+        .align_y(iced::alignment::Vertical::Center)
+        .into()
+    } else {
+        text("FRIENDS").size(14).color(color_text).into()
+    };
 
     container(
         column![
-            text("FRIENDS").size(if has_friends { 18 } else { 14 }).color(color_text),
+            title_row,
             intro,
             vertical_space(if has_friends { 10.0 } else { 4.0 }),
             readonly_warning,