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/Cargo.toml

@@ -13,6 +13,11 @@ path = "src/main.rs"
 breadpad-shared = { path = "../breadpad-shared" }
 # Capture primitives for `--screenshot` mode — see src/screenshot.rs.
 bread-screenshots = { git = "https://git.breadway.dev/Breadway/bread-ecosystem", branch = "dev" }
+# libadwaita-based settings-screen components (see src/views/settings.rs) —
+# on "dev", not breadpad-shared's tag-pinned copy, since the `adw` feature
+# doesn't exist on a tagged release yet.
+bread-theme = { git = "https://git.breadway.dev/Breadway/bread-ecosystem", branch = "dev", features = ["adw"] }
+libadwaita = { version = "0.9", features = ["v1_7"] }
 anyhow.workspace = true
 tracing.workspace = true
 tracing-subscriber.workspace = true