feat(ads): wire real AdMob ids (Phase 5 finalize)

Replaces the TODO_REAL_* ad-unit placeholders with the owner's real AdMob
console ids (publisher pub-5605900229781491) and the native AdMob app ids
(iOS ~8397095848, Android ~8257495040) in place of the Google sample ids.
Debug builds still serve Google test ads via kDebugMode; release builds now
use the real units.

android/app/src/main/AndroidManifest.xml

@@ -27,7 +27,7 @@
         </activity>
         <meta-data
             android:name="com.google.android.gms.ads.APPLICATION_ID"
-            android:value="ca-app-pub-3940256099942544~3347511713"/>
+            android:value="ca-app-pub-5605900229781491~8257495040"/>
         <!-- Don't delete the meta-data below.
              This is used by the Flutter tool to generate GeneratedPluginRegistrant.java -->
         <meta-data