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/build.gradle.kts

@@ -7,19 +7,18 @@ buildscript {
         mavenCentral()
     }
     dependencies {
-        classpath("com.google.gms:google-services:4.4.2")
+        classpath("com.google.gms:google-services:4.5.0")
     }
 }
 
 plugins {
-    kotlin("multiplatform") version "2.1.0" apply false
-    kotlin("android") version "2.1.0" apply false
-    kotlin("jvm") version "2.1.0" apply false
-    kotlin("plugin.serialization") version "2.1.0" apply false
-    id("com.android.application") version "8.7.3" apply false
-    id("com.android.library") version "8.7.3" apply false
-    id("org.jetbrains.compose") version "1.7.3" apply false
-    id("org.jetbrains.kotlin.plugin.compose") version "2.1.0" apply false
+    kotlin("multiplatform") version "2.4.10" apply false
+    kotlin("jvm") version "2.4.10" apply false
+    kotlin("plugin.serialization") version "2.4.10" apply false
+    id("com.android.application") version "9.3.1" apply false
+    id("com.android.kotlin.multiplatform.library") version "9.3.1" apply false
+    id("org.jetbrains.compose") version "1.11.1" apply false
+    id("org.jetbrains.kotlin.plugin.compose") version "2.4.10" apply false
 }
 
 tasks.register("clean") {