Model calls now time out (75s default, AI_REQUEST_TIMEOUT_MS) via AbortController,
instead of hanging for minutes on a slow/overloaded model. A timeout surfaces a clear
"took too long — try again or switch to a faster model" message.
"Make it more detailed" now edits the board. The actions spec treats expand / flesh-out
/ add-detail requests on an existing diagram as edit intents — the assistant adds the
cards/connections directly instead of writing an essay and asking permission.
