Initialize Rust GPUI browser shell

crates/ely_servo_host/src/error.rs

@@ -0,0 +1,11 @@
+use ely_domain::WebViewId;
+use thiserror::Error;
+
+#[derive(Clone, Debug, Error, Eq, PartialEq)]
+pub enum ServoHostError {
+    #[error("webview not found: {id}")]
+    WebViewNotFound { id: WebViewId },
+
+    #[error("permission request missing profile context")]
+    MissingProfileContext,
+}