feat(delegate-task): ⚙️ make sync subagent timeout configurable via syncPollTimeoutMs

Allow users to set `background_task.syncPollTimeoutMs` in config to override
the default 10-minute sync subagent timeout. Affects sync task, sync continuation,
and unstable agent task paths. Minimum value: 60000ms (1 minute).

Co-authored-by: Wine Fox <fox@ling.plus>

src/tools/delegate-task/timing.ts

@@ -6,6 +6,8 @@ let WAIT_FOR_SESSION_TIMEOUT_MS = 30000
 let MAX_POLL_TIME_MS = 10 * 60 * 1000
 let SESSION_CONTINUATION_STABILITY_MS = 5000
 
+export const DEFAULT_SYNC_POLL_TIMEOUT_MS = 600_000
+
 export function getTimingConfig() {
   return {
     POLL_INTERVAL_MS,