Update dependencies to latest + migrate to AGP 9.x

Kotlin 2.1.0->2.4.10, Compose Multiplatform 1.7.3->1.11.1, AGP 8.7.3->9.3.1, Gradle 8.10.2->9.7.1. The two libs that pinned us to Compose 1.7.x -- compose-webview-multiplatform (1.9.40->2.0.3) and multiplatform-markdown-renderer (0.33.0->0.44.0) -- now have Compose 1.8+ releases, so the whole stack moves. Also coroutines/serialization 1.11.0, okhttp 5.5.0, media3 1.11.0, activity-compose 1.13.0, firebase-messaging 25.1.2, compose-bom 2026.08.00, google-services 4.5.0, KCEF 2025.03.23 (JBR pin ->17.0.14); material3 1.9.0 / material-icons-extended 1.7.3 (each one's latest stable -- they lag the core).

AGP 9 migration: :shared swaps com.android.library->com.android.kotlin.multiplatform.library (android config moves into kotlin{android{}}, withHostTest{} keeps host tests); :androidApp drops kotlin(android) for AGP 9 built-in Kotlin. compileSdk 34->37 (minSdk stays 29 / Android 10).

Code fixes for API breaks: markdown link->textLink + highlights->highlightsBuilder; kotlinOptions{jvmTarget}->compilerOptions{jvmTarget}.

app/androidApp/build.gradle.kts

@@ -1,12 +1,13 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
 plugins {
     id("com.android.application")
-    kotlin("android")
     id("org.jetbrains.kotlin.plugin.compose")
 }
 
 android {
     namespace = "dev.iris.app"
-    compileSdk = 34
+    compileSdk = 37
 
     defaultConfig {
         applicationId = "dev.iris.app"
@@ -26,18 +27,20 @@ android {
         sourceCompatibility = JavaVersion.VERSION_17
         targetCompatibility = JavaVersion.VERSION_17
     }
+}
 
-    kotlinOptions {
-        jvmTarget = "17"
+kotlin {
+    compilerOptions {
+        jvmTarget.set(JvmTarget.JVM_17)
     }
 }
 
 dependencies {
     implementation(project(":shared"))
-    implementation(platform("androidx.compose:compose-bom:2024.09.02"))
+    implementation(platform("androidx.compose:compose-bom:2026.08.00"))
     implementation("androidx.compose.material3:material3")
     implementation("androidx.compose.ui:ui")
-    implementation("androidx.activity:activity-compose:1.9.2")
+    implementation("androidx.activity:activity-compose:1.13.0")
     implementation("androidx.core:core-splashscreen:1.0.1")
 }