feat: make MCP server registrations persistent across peer disconnects

Persistent MCP servers (opt-in via `persistent: true`) survive host
disconnects — they appear as offline in mcp_list and auto-restore when
the host reconnects. Ephemeral servers (default) still clean up on
disconnect. Offline servers return a clear error on mcp_call with
time-since-disconnect info.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/cli/src/ws/client.ts

@@ -931,6 +931,7 @@ export class BrokerClient {
     serverName: string,
     description: string,
     tools: Array<{ name: string; description: string; inputSchema: Record<string, unknown> }>,
+    persistent?: boolean,
   ): Promise<{ serverName: string; toolCount: number } | null> {
     if (!this.ws || this.ws.readyState !== this.ws.OPEN) return null;
     return new Promise((resolve) => {
@@ -938,7 +939,7 @@ export class BrokerClient {
       this.mcpRegisterResolvers.set(reqId, { resolve, timer: setTimeout(() => {
         if (this.mcpRegisterResolvers.delete(reqId)) resolve(null);
       }, 5_000) });
-      this.ws!.send(JSON.stringify({ type: "mcp_register", serverName, description, tools, _reqId: reqId }));
+      this.ws!.send(JSON.stringify({ type: "mcp_register", serverName, description, tools, ...(persistent ? { persistent: true } : {}), _reqId: reqId }));
     });
   }