Add a spec review gate to PlanExecEngine that pauses execution after the
first Spec is generated, awaiting the user's confirm/reject decision.
On approval execution continues; on rejection the engine replans (capped
at 2 replans); on 30-min timeout the Spec is parked (not failed) so the
user can resume later.
- spec_manager: add parked status + park()/resume() methods
- plan_exec_engine: add spec_review_handler param, wire gate into both
execute_stream and _execute_loop with replan cap, emit
spec_review_request/spec_review_reply events, handle timeout to park
- chat.py: whitelist new events, add spec_review_reply WS handler,
wire _spec_review_handler closure (30-min timeout), cleanup on disconnect
- portal.py: persist spec_review_id/decision/feedback for page reload
- tests: 20 unit tests covering happy path, rejection/replan, timeout,
cancellation, backward compat, handler errors, park/resume round-trips
chiguyong