breadman: rebuild settings with libadwaita components

Proof-of-concept for the ecosystem-wide design-system work: every setting
is now an AdwPreferencesGroup/SwitchRow/SpinRow/ActionRow/ComboRow via
bread-theme::adw, instead of a hand-rolled GtkGrid of labels + raw widgets.

This directly fixes the two worst defects a design critique found here:
- Toggle switches rendered ~1400px wide, like progress bars — caused by
  GtkGrid sizing a switch's column to match a sibling entry's hexpand in
  the same grid, and Switch has no default that resists filling that
  width. AdwSwitchRow owns its own layout, so this class of bug can't
  recur.
- Spin buttons were ~1300px from the label they modified, for the same
  grid-column-sizing reason. AdwSpinRow docks the spinner to its title.

Also softened the jargon-forward section titles the critique flagged
("Model (Tier 2 ONNX)", "Ollama (Tier 3)") — the tier/implementation
detail moved from the title (loud, unavoidable) to each group's
description (quieter, still there for anyone who wants it).

bread-theme now needs a direct dependency here (branch=dev, `adw`
feature) since breadpad-shared's own bread-theme dependency is tag-pinned
to a release before this feature existed.

breadman/src/main.rs

@@ -342,6 +342,10 @@ fn build_app_window(
     screenshot_req: Option<screenshot::ScreenshotRequest>,
 ) -> Result<()> {
     apply_css(&cfg);
+    // Needed once before constructing any adw:: widget (see views::settings) —
+    // also forces dark mode, since bread-theme's palette is a fixed dark base
+    // regardless of the system GTK preference.
+    bread_theme::adw::init();
 
     let store = Arc::new(Store::new()?);
     let notes = store.load_all()?;