chore: get Android project building (toolchain, deps, manifest, launcher icon)

- Fix dependency versions (Retrofit 2.11, OkHttp 4.12, Compose BOM)
- Add Material Components for the app theme
- Add --add-exports/--add-opens for kapt on JDK 21
- Remove deprecated manifest package attr; add INTERNET permission
- Add adaptive launcher icon

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

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

@@ -0,0 +1,5 @@
+<resources>
+    <style name="Theme.Calendarr" parent="Theme.Material3.DayNight.NoActionBar">
+        <item name="android:windowBackground">?android:colorBackground</item>
+    </style>
+</resources>