feat: add platform OAuth implementations (Android, iOS, Desktop)

- AndroidOAuthClient: ACTION_VIEW + OAuthCallbackActivity (myice://callback)
- IosOAuthClient: ASWebAuthenticationSession with presentation context provider
- DesktopOAuthClient: local HTTP server + system browser
- AndroidManifest: register OAuthCallbackActivity intent filter
- Align Kotlin to 2.3.20 (required by Compose MP 1.11.1 klibs) and
  compileSdk to 36 (required by activity-compose 1.13.0); fix missing
  Text import and stray brace in placeholder iOS/Android entry points

composeApp/src/androidMain/AndroidManifest.xml

@@ -15,6 +15,17 @@
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
         </activity>
+        <activity
+            android:name=".OAuthCallbackActivity"
+            android:exported="true"
+            android:launchMode="singleTask">
+            <intent-filter>
+                <action android:name="android.intent.action.VIEW" />
+                <category android:name="android.intent.category.DEFAULT" />
+                <category android:name="android.intent.category.BROWSABLE" />
+                <data android:scheme="myice" android:host="callback" />
+            </intent-filter>
+        </activity>
     </application>
 
 </manifest>