Add on-screen diagnostics to the Logs tab

Without adb there was no way to see why vehicle values stay blank:
refreshVehicle() swallowed every exception. The Logs tab now shows the
package, version, UID (and whether it is the system UID), signer
SHA-256, firmware, car permission grants, the last snapshot and read
error, and the newest 200 entries of the vehicle library's AppLogger.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

SPECS.md

@@ -42,6 +42,8 @@ what has been changed, and what is still to do.
 - 2026-10-17 — Renamed to "Nils' MG4": package ID `com.stinnesbeck.nilsmg4` (`.unstable` for the car
   build), APK names `NilsMG4-*.apk`. It installs next to the old FatihsMG4 app instead of replacing
   it, and starts with empty settings and history.
+- 2026-10-17 — Diagnostics section on the Logs tab: UID, signer, car permissions, last vehicle
+  read and its error, and the vehicle library's in-app log. For debugging without adb.
 
 ## Installing on the car