i18n: offer French and Polish in the language picker

Both landed as community translations through Weblate (French ~33%, Polish
~57%), above the bar already shipped for zh-CN. Add them to locales_config.xml —
the single source of truth for the in-app language picker and Android's per-app
language settings.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/src/main/res/xml/locales_config.xml

@@ -11,6 +11,8 @@
     <locale android:name="en" />
     <locale android:name="de" />
     <locale android:name="es" />
+    <locale android:name="fr" />
     <locale android:name="it" />
+    <locale android:name="pl" />
     <locale android:name="zh-CN" />
 </locale-config>