0.6.2: add Bluetooth panel

Adapter power switch, paired devices (connect/disconnect/forget), and
scan-for-new-devices with pairing -- BOS had bluez/bluez-utils packaged
and bread's own daemon already monitors Bluetooth events, but there was
no GUI to actually manage devices anywhere in the settings app.

Shells out to bluetoothctl's non-interactive mode, same "standard CLI,
no new dependency" choice as Network (nmcli) and Snapshots (snapper).
Pairing only covers "just works" SSP (most audio/HID devices) -- a
device requiring a PIN would need this app to register its own
bluetoothd agent, out of scope for now; it just fails with the reason
shown, same honest-failure pattern the Firewall fix added.

src/ui/views/mod.rs

@@ -2,6 +2,7 @@ pub mod about;
 pub mod appearance;
 pub mod aur;
 pub mod autostart;
+pub mod bluetooth;
 pub mod bread;
 pub mod breadbar;
 pub mod breadbox;