chore: senior-review cleanup pass

- Remove Gemini's committed update_*.py regex-surgery scripts
- Drop unused iroh-tickets dependency (hand-rolled ticket is used instead)
- Replace ToString antipattern with Display impl on PeerSpeakTicket
- Route debug log to XDG state/cache dir instead of hardcoded /home path
- Clear all compiler + clippy warnings (unused imports, collapsible ifs,
  redundant pattern matching, missing Default)

Builds clean with zero warnings.

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

src/app/mod.rs

@@ -4,7 +4,7 @@ use crate::audio::pw_cli::{AudioDevice, enumerate_audio_devices};
 use crate::config::AppConfig;
 
 use iced::widget::{
-    container, column, row, text, button, text_input, scrollable, slider, checkbox, pick_list, Column, Space,
+    container, column, row, text, button, text_input, scrollable, slider, checkbox, pick_list, Column,
 };
 use iced::{
     Color, Background, Border, Element, Subscription, Task, Theme, Event, keyboard,
@@ -143,7 +143,7 @@ pub fn run_gui() -> iced::Result {
         .run()
 }
 
-fn subscription(state: &AppState) -> Subscription<AppMessage> {
+fn subscription(_state: &AppState) -> Subscription<AppMessage> {
     let core_sub = Subscription::run(core_subscription).map(AppMessage::UiEventReceived);
     let event_sub = iced::event::listen().map(AppMessage::EventOccurred);
     Subscription::batch(vec![core_sub, event_sub])