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/shared/src/commonMain/kotlin/iris/IrisApp.kt

@@ -0,0 +1,53 @@
+package iris
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Surface
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+
+/**
+ * Root composable shared by the Android and Desktop shells.
+ *
+ * M0: a visible placeholder to confirm the Compose stack renders. M1+
+ * replaces this with the Connect screen, chat UI, and the rest of the app
+ * (see docs/10-android-app.md).
+ */
+@Composable
+fun IrisApp() {
+    MaterialTheme {
+        Surface(modifier = Modifier.fillMaxSize()) {
+            Box(
+                modifier = Modifier
+                    .fillMaxSize()
+                    .background(Color(0xFF1B1E28)),
+                contentAlignment = Alignment.Center,
+            ) {
+                Column(horizontalAlignment = Alignment.CenterHorizontally) {
+                    Box(
+                        modifier = Modifier
+                            .size(72.dp)
+                            .background(Color(0xFF4F7CFF), CircleShape),
+                        contentAlignment = Alignment.Center,
+                    ) {
+                        Text(text = "I", color = Color.White, fontSize = 40.sp)
+                    }
+                    Spacer(modifier = Modifier.height(16.dp))
+                    Text(text = "Iris × Hermes", color = Color.White, fontSize = 22.sp)
+                }
+            }
+        }
+    }
+}