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/shared/src/commonMain/kotlin/iris/ui/MarkdownText.kt

@@ -157,7 +157,9 @@ fun MarkdownText(
             ordered = base,
             bullet = base,
             list = base,
-            link = base.copy(textDecoration = TextDecoration.Underline),
+            textLink = TextLinkStyles(
+                style = base.copy(textDecoration = TextDecoration.Underline).toSpanStyle(),
+            ),
             table = base.copy(fontSize = fontSize * 0.95f),
         ),
         components = markdownComponents(
@@ -207,7 +209,7 @@ internal fun CodeBlockWithCopy(
 ) {
     val clipboard = LocalClipboardManager.current
     Box {
-        MarkdownHighlightedCode(code = code, language = language, highlights = highlights, style = style)
+        MarkdownHighlightedCode(code = code, language = language, highlightsBuilder = highlights, style = style)
         if (code.isNotBlank()) {
             IconButton(
                 onClick = { clipboard.setText(AnnotatedString(code)) },

app/shared/src/desktopMain/kotlin/iris/platform/DesktopWebView.kt

@@ -38,11 +38,11 @@ private suspend fun ensureKcefInitialized() {
         KCEF.init(
             builder = {
                 installDir(File(System.getProperty("user.home"), ".iris/kcef-bundle"))
-                // Pinned to the JBR 17 release the KCEF 2024.04.20.x line was
+                // Pinned to the JBR 17 release the KCEF 2025.03.23 line is
                 // built against; the default "latest" JBR may be JDK 21-based
                 // and is not guaranteed compatible.
                 download {
-                    github { release("jbr-release-17.0.12b1207.37") }
+                    github { release("jbr-release-17.0.14b1367.22") }
                 }
                 settings {
                     cachePath = File(System.getProperty("user.home"), ".iris/kcef-cache").absolutePath