feat(identity): copy-to-clipboard button for the node ID (W7)

The Identity section showed only a truncated id and iced text isn't
selectable, so there was no way to share your full node id. Add a Copy
button (mirrors the room-ticket copy) that writes the FULL id to the
clipboard via a new generic CopyText(String) message. Also unblocks the
add-a-friend self-test (copy your id, paste into Add friend).

256 lib tests green, clippy clean, release builds.

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

src/app/mod.rs

@@ -117,6 +117,8 @@ pub enum AppMessage {
     ToggleDeafenPressed,
     UiEventReceived(UiEvent),
     CopyToClipboard,
+    /// Copy an arbitrary string to the clipboard (e.g. the full node ID).
+    CopyText(String),
     TogglePtt(bool),
     StartSettingHotkey,
     PeerVolumeChanged(EndpointId, f32),
@@ -691,6 +693,9 @@ fn update(state: &mut AppState, message: AppMessage) -> Task<AppMessage> {
                 return iced::clipboard::write(state.ticket.clone());
             }
         }
+        AppMessage::CopyText(s) => {
+            return iced::clipboard::write(s);
+        }
         AppMessage::TogglePtt(enabled) => {
             state.ptt_enabled = enabled;
             let _ = state.controller.send(CoreCommand::SetPttMode(enabled));
@@ -1549,13 +1554,35 @@ fn view(state: &AppState) -> Element<'_, AppMessage> {
             })
             .into()
         };
+        // The ID line shows a short form (iced text isn't selectable) plus a Copy
+        // button that puts the FULL node id on the clipboard, so it's shareable.
+        let id_row: Element<AppMessage> = match state.self_node_id.clone() {
+            Some(full) => row![
+                text(format!("ID: {id_display}")).size(13).color(color_text),
+                button(
+                    row![
+                        icon(IconKind::Copy, 13.0, color_text),
+                        text("Copy").size(12),
+                    ]
+                    .spacing(5)
+                    .align_y(iced::alignment::Vertical::Center)
+                )
+                .on_press(AppMessage::CopyText(full))
+                .style(b_style(color_surface, color_blue, color_text, 6.0))
+                .padding(6),
+            ]
+            .spacing(10)
+            .align_y(iced::alignment::Vertical::Center)
+            .into(),
+            None => text(format!("ID: {id_display}")).size(13).color(color_text).into(),
+        };
         let identity_section = column![
             text("Your permanent ID — friends recognise you by this. It stays the \
                   same across launches; regenerate only to start fresh as a new \
                   identity (friends who saved the old one will no longer reach you).")
                 .size(12)
                 .color(color_subtext),
-            text(format!("ID: {id_display}")).size(13).color(color_text),
+            id_row,
             button(text("Regenerate identity").size(13))
                 .on_press(AppMessage::OpenRegenerateIdentityConfirm)
                 .style(b_style(color_surface, color_maroon, color_text, 6.0))