fix(build): unblock SDK 56 Android + iOS builds

- app.json: kotlinVersion 2.0.21 -> 2.1.20 (Expo SDK 56 modules require >= 2.1.20)
- re-add @react-navigation/native: it is a peer dependency of
  @bottom-tabs/react-navigation and was wrongly removed; its absence broke the
  iOS eager JS bundle (expo export:embed) during the native build.

Local `expo export -p ios` now bundles cleanly. SDK 56 disables USE_FRAMEWORKS
for RNScreens/ReactCodegen, which resolves the original signed-iOS RNScreens
static-frameworks build failure.

app.json

@@ -86,7 +86,7 @@
             "compileSdkVersion": 36,
             "targetSdkVersion": 35,
             "buildToolsVersion": "35.0.0",
-            "kotlinVersion": "2.0.21",
+            "kotlinVersion": "2.1.20",
             "minSdkVersion": 26,
             "usesCleartextTraffic": true,
             "packagingOptions": {