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/mcp/tools.ts

@@ -682,6 +682,10 @@ export const TOOLS: Tool[] = [
           },
           description: "Tool definitions to expose",
         },
+        persistent: {
+          type: "boolean",
+          description: "If true, registration survives peer disconnect. Other peers see it as 'offline' until you reconnect. Default: false",
+        },
       },
       required: ["server_name", "description", "tools"],
     },