feat(gui): replace settings ⚙ placeholder with Bootstrap cog icon

Add iced_aw + iced_fonts (bootstrap feature) to load the Bootstrap Icons
font. The settings button and settings header now render the gear-fill
glyph (U+F3F8) via text("\u{F3F8}").font("bootstrap-icons") instead of
the raw ⚙ character which was not in iced's bundled Inter font.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/gui.rs

@@ -611,7 +611,7 @@ fn view(state: &Dashboard) -> Element<'_, Message> {
         return view_settings(state);
     }
 
-    let settings_btn = button(text("⚙").size(16))
+    let settings_btn = button(text("\u{F3F8}").font(iced::Font::with_name("bootstrap-icons")).size(16))
         .on_press(Message::ShowSettings)
         .style(button::secondary);
 
@@ -1086,7 +1086,7 @@ fn diagnose_card<'a>(
 
 fn view_settings(state: &Dashboard) -> Element<'_, Message> {
     let header = row![
-        text("⚙  Settings").size(24),
+        row![text("\u{F3F8}").font(iced::Font::with_name("bootstrap-icons")).size(20), text("  Settings").size(24)].align_y(Alignment::Center),
         iced::widget::horizontal_space(),
         button(text("← Back").size(13))
             .on_press(Message::HideSettings)
@@ -1167,6 +1167,7 @@ pub fn run(config: &Config) -> Result<()> {
     iced::application(|_: &Dashboard| String::from("umutray"), update, view)
         .subscription(subscription)
         .theme(|_| Theme::Dark)
+        .font(iced_aw::iced_fonts::BOOTSTRAP_FONT_BYTES)
         .window(iced::window::Settings {
             size: iced::Size::new(600.0, 560.0),
             ..Default::default()