Discover MCP servers, split into tool groups and unavailable servers.
Best-effort: if discovery itself raises (no config, offline, load error),
the technical detail is logged and a generic mcp_error message is
returned so dcode tools list still renders the built-in tools while
telling the user discovery failed. Servers that loaded but expose no tools
are reported as UnavailableServers (errored, needing login, or disabled)
rather than silently dropped — surfacing exactly what a user running this
command to debug a missing tool needs to see.
Explicit MCP config path (--mcp-config), or None
to rely on auto-discovery.
Project-level stdio trust decision
(--trust-project-mcp), forwarded to discovery unchanged.
