feat(presence): presence-mode selector in Settings (W7 P5)

Add a 'Presence' section to Settings with three radio options wired to the
persisted PresenceMode (W7): Normal (friends only, no beacon; default),
Invisible (appear offline to everyone), Discoverable (also publish so friends
can find you after a network change). Each has a hover tooltip explainer,
mirroring the recording-mode radios.

Selecting one saves config.presence_mode. The live friends listener (P4, not
yet wired) will read this posture when it lands; no core command until then.

256 lib tests green, clippy clean, release builds. Solo screenshot-verifiable
(the live effect needs P4 + 2 machines).

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

src/app/mod.rs

@@ -3,6 +3,7 @@ use crate::network::PeerState;
 use crate::notify::{self, Sound};
 use crate::audio::pw_cli::{AudioDevice, enumerate_audio_devices};
 use crate::config::{AppConfig, NetworkMode, RecordingMode, RoomLayout};
+use crate::presence::PresenceMode;
 use crate::theme::{AppTheme, Palette};
 
 use iced::widget::{
@@ -135,6 +136,8 @@ pub enum AppMessage {
     NoiseGateDragging(f32),
     NetworkModeSelected(NetworkMode),
     RecordingModeSelected(RecordingMode),
+    /// Choose the friends presence posture (W7): invisible / normal / discoverable.
+    PresenceModeSelected(PresenceMode),
     EventOccurred(Event),
     NavigateToSettings,
     NavigateBack,
@@ -733,6 +736,12 @@ fn update(state: &mut AppState, message: AppMessage) -> Task<AppMessage> {
             // Takes effect on the next recording start.
             let _ = state.controller.send(CoreCommand::SetRecordingMode(mode));
         }
+        AppMessage::PresenceModeSelected(mode) => {
+            state.config.presence_mode = mode;
+            state.config.save();
+            // Persisted now; the live friends listener (P4, not yet wired) reads
+            // this posture when it lands. No core command until then.
+        }
         AppMessage::ToggleNotifications(enabled) => {
             state.config.notifications_enabled = enabled;
             state.config.save();
@@ -1009,6 +1018,21 @@ fn recording_mode_hint(mode: RecordingMode) -> &'static str {
     }
 }
 
+/// One-line explanation of a presence posture for the settings picker (W7).
+fn presence_mode_hint(mode: PresenceMode) -> &'static str {
+    match mode {
+        PresenceMode::Invisible => {
+            "Answer no one — appear offline to everyone, even friends."
+        }
+        PresenceMode::Normal => {
+            "Answer friends only, from your saved address. No presence beacon."
+        }
+        PresenceMode::Discoverable => {
+            "Also publish so friends can still find you after you change networks (opt-in)."
+        }
+    }
+}
+
 /// Formats a call duration as `m:ss` (or `h:mm:ss` past an hour).
 fn format_duration(total_secs: u64) -> String {
     let h = total_secs / 3600;
@@ -1475,6 +1499,30 @@ fn view(state: &AppState) -> Element<'_, AppMessage> {
             identity_warning,
         ].spacing(8).width(iced::Length::Fill);
 
+        // --- Presence (W7) — how reachable you are to friends while idle. ---
+        let presence_radio = |mode: PresenceMode, label: &'static str| -> Element<'_, AppMessage> {
+            tooltip(
+                radio(label, mode, Some(state.config.presence_mode), AppMessage::PresenceModeSelected),
+                container(text(presence_mode_hint(mode)).size(11).color(color_text))
+                    .padding(8)
+                    .max_width(320.0)
+                    .style(c_style(color_crust, color_surface, 6.0)),
+                iced::widget::tooltip::Position::Right,
+            )
+            .gap(8)
+            .into()
+        };
+        let presence_section = column![
+            text("Controls whether friends can see you're online (and what room \
+                  you're in) while the app is open. Discovery stays off unless you \
+                  pick Discoverable.")
+                .size(12)
+                .color(color_subtext),
+            presence_radio(PresenceMode::Normal, "Normal — friends only, no beacon"),
+            presence_radio(PresenceMode::Invisible, "Invisible — appear offline"),
+            presence_radio(PresenceMode::Discoverable, "Discoverable — findable after a network change"),
+        ].spacing(8).width(iced::Length::Fill);
+
         let settings_content = scrollable(
             column![
                 // --- Audio Devices ---
@@ -1571,6 +1619,11 @@ fn view(state: &AppState) -> Element<'_, AppMessage> {
                 identity_section,
                 vertical_space(section_gap),
 
+                // --- Presence ---
+                section_header("Presence"),
+                presence_section,
+                vertical_space(section_gap),
+
                 // --- Notifications & Sounds ---
                 section_header("Notifications & Sounds"),
                 column![