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>

app/src/main/res/values/strings.xml

@@ -107,6 +107,8 @@
     <!-- Call log -->
     <string name="label_call_log">Recent uploads</string>
     <string name="call_log_empty">No upload attempted yet.</string>
+    <string name="label_diagnostics">Diagnostics</string>
+    <string name="btn_refresh_diagnostics">Refresh diagnostics</string>
     <string name="btn_flush_now">Upload now</string>
     <string name="status_starting">Starting…</string>
     <string name="status_running_no_upload">Running — waiting for first upload</string>