fix(bluetooth): add passkey/PIN display dialogs for keyboard pairing

Bluetooth keyboards require the host to display a passkey for the user
to type. Previously this was not supported because the agent capability
was set to DisplayYesNo and the DisplayPasskey/DisplayPinCode events
were not handled.

- Change agent capability to KeyboardDisplay
- Add DisplayPasskey dialog with typed-key progress indicator
- Add DisplayPinCode dialog for older keyboards
- Auto-dismiss display dialogs when device reports Paired=true

subscriptions/bluetooth/src/agent.rs

@@ -40,7 +40,7 @@ pub async fn watch(
     bluez
         .register_agent(
             &agent_path,
-            <&'static str>::from(bluez_zbus::agent1::Capability::DisplayYesNo),
+            <&'static str>::from(bluez_zbus::agent1::Capability::KeyboardDisplay),
         )
         .await?;