Rename package and APKs to NilsMG4, credit Fatih, add SPECS.md

- applicationId com.evsuite.abrp -> com.stinnesbeck.nilsmg4 (the car
  build is .unstable); the Java namespace is unchanged. Installs next to
  upstream's app rather than over it.
- APK names NilsMG4-*.apk, debug builds included; build-car follows.
- OTA install-result action, cache/download names, User-Agent and log
  tags follow the new name.
- About credits fatihdonmezdev / FatihsMG4.
- SPECS.md journals what changed and what is still to do, starting
  with pointing the About link and QR code at git.stinnesbeck.com/nils/mg4.

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

app/src/unstable/AndroidManifest.xml

@@ -27,7 +27,7 @@
             android:name=".OtaInstallResultReceiver"
             android:exported="false">
             <intent-filter>
-                <action android:name="com.evsuite.abrp.OTA_INSTALL_RESULT" />
+                <action android:name="com.stinnesbeck.nilsmg4.OTA_INSTALL_RESULT" />
             </intent-filter>
         </receiver>
     </application>