fix: lazy agent loading and type safety improvements

1. Lazy agent loading - fix race condition where prompts sent before initialization completes:
   - Add ensureAgentLoaded() helper that deduplicates initialization requests
   - Update handleSendAgentMessage/Audio to await agent initialization before streaming
   - Fix status updates being sent to client after initialization

2. Type safety - remove unsafe 'as any' casts for agent status:
   - Create AGENT_LIFECYCLE_STATUSES constant as single source of truth
   - Export AgentStatusSchema from messages.ts for reuse
   - Update registry schema to validate lastStatus against AgentStatusSchema
   - Add .default("closed") to handle missing status values from legacy files
   - Remove (record.lastStatus as any) cast in buildStoredAgentPayload

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

packages/server/src/server/agent/agent-manager.ts

@@ -22,12 +22,16 @@ import type {
 } from "./agent-sdk-types.js";
 import { resolveAgentModel } from "./model-resolver.js";
 
+export const AGENT_LIFECYCLE_STATUSES = [
+  "initializing",
+  "idle",
+  "running",
+  "error",
+  "closed",
+] as const;
+
 export type AgentLifecycleStatus =
-  | "initializing"
-  | "idle"
-  | "running"
-  | "error"
-  | "closed";
+  (typeof AGENT_LIFECYCLE_STATUSES)[number];
 
 export type AgentSnapshot = {
   id: string;