Voice assistant, vehicle data, and template rendering fixes

Push-to-talk voice control, gated behind experimental settings alongside a new raw vehicle sensor screen. Spotify now shows as partial instead of working since its browse tile rejects Gearslip as a host. Fixed a gap where a live nav app couldn't take a fresh destination without a full reconnect.

README.md

@@ -13,9 +13,6 @@ and Gearslip renders that template natively on the car screen. Nothing is mirror
 the phone. For apps without a car interface, Gearslip offers a separate screen-sharing
 mode.
 
-The author reverse-engineered the protocol for interoperability, so that a client other
-than Google's own can talk to a car head unit.
-
 ## Features
 
 - **Phone calls.** Dial from a keypad, or search your contacts, then confirm before the