feat: display agent avatar from OpenClaw identity config

Fetch agent identity via agent.identity.get WS method after connect.
Display avatar in message bubbles (replacing Bot icon) and in the
header (replacing the PinchChat logo when an avatar is configured).
Falls back to default icons when no avatar is set.

src/types/index.ts

@@ -35,6 +35,13 @@ export interface Session {
   lastMessagePreview?: string;
 }
 
+export interface AgentIdentity {
+  name?: string;
+  emoji?: string;
+  avatar?: string;
+  agentId?: string;
+}
+
 export type ConnectionStatus = 'disconnected' | 'connecting' | 'connected';
 
 export interface GatewayState {