M0: toolchain, monorepo scaffold, gateway plugin skeleton, CMP app

- gateway-plugin/: android platform plugin (plugin.yaml + adapter.py
  register(ctx) + no-op AndroidAdapter) + stub modules for M1-M5
- app/: Compose Multiplatform project (shared KMP + androidApp +
  desktopApp) with Gradle wrapper; builds :androidApp:assembleDebug
  and :desktopApp:compileKotlin
- scripts/guard_hermes_agent.sh + pre-commit hook: fail if hermes-agent/
  is staged (read-only reference, never committed)
- .gitignore excludes hermes-agent/; docs/ reference library

app/desktopApp/build.gradle.kts

@@ -0,0 +1,27 @@
+import org.gradle.internal.os.OperatingSystem
+
+plugins {
+    kotlin("jvm")
+    id("org.jetbrains.compose")
+    id("org.jetbrains.kotlin.plugin.compose")
+}
+
+val composeVersion = "1.7.3"
+val os = OperatingSystem.current()
+val arch = System.getProperty("os.arch") ?: "amd64"
+val desktopTarget = when {
+    os.isMacOsX -> if (arch == "aarch64") "macos-arm64" else "macos-x64"
+    os.isWindows -> "windows-x64"
+    else -> if (arch == "aarch64") "linux-arm64" else "linux-x64"
+}
+
+dependencies {
+    implementation(project(":shared"))
+    implementation("org.jetbrains.compose.desktop:desktop-jvm-$desktopTarget:$composeVersion")
+}
+
+compose.desktop {
+    application {
+        mainClass = "iris.desktop.MainKt"
+    }
+}