App 2.19.2: Full screen for CarPlay (experiment)

Adds com.allgo.carplay.service to immersive.full in Android 9's
policy_control setting when switched on, removes only that entry when
off. Car build (system user) only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LhzAVaUyqcw5PkGjz4mWW6

AGENTS.md

@@ -35,7 +35,9 @@ Repository: `ssh://git@git.stinnesbeck.com:2222/nils/mg4.git` (remote `origin`),
    `secrets.example.yaml` holds `CHANGE-ME` placeholders only. Stage files explicitly, check the
    index for changes that are not yours (the owner works in parallel), and scan the staged diff
    for secrets before every commit. Never print a token.
-3. **Telemetry is read-only.** The app never writes a vehicle setting.
+3. **Telemetry is read-only.** The app never writes a vehicle setting. The one system setting it
+   writes is `policy_control` (CarPlay full screen), only when the driver switches it on, and only
+   its own entry.
 4. **A failed read is not a zero.** Unreadable values are `null`, omitted from payloads and
    shown as "—". Sending 0 for SOC tells ABRP the battery is empty.
 5. **Fail closed.** Updates (origin, SHA-256, package, signature), credentials, unknown state.
@@ -66,7 +68,7 @@ Repository: `ssh://git@git.stinnesbeck.com:2222/nils/mg4.git` (remote `origin`),
 | Consumption / Charging | period totals, daily log, charging sessions and curve |
 | Live data | on/off, ABRP API key and user token, upload frequency |
 | Server | URL, pairing by QR, ingest token, installation ID (read-only), config import |
-| Settings | full screen, voice key, tyre unit, accent colour, battery, charging price, version, update check, install from USB, About |
+| Settings | full screen, voice key, CarPlay full screen (experiment), tyre unit, accent colour, battery, charging price, version, update check, install from USB, About |
 | Logs | upload log |
 
 Key classes (`app/src/main/java/com/evsuite/abrp/`): `AbrpUploadService` (foreground service,