Add _record_dashboard_proxy_event, _settle_market_result,
_get_market_source_details, _market_request_id and
_extract_usage_from_sse_chunk to RotationHandler, and the market
settlement cluster to AutoselectHandler. These were defined only on
RequestHandler, so rotation/autoselect requests raised AttributeError
(crash on the dashboard event path, silently swallowed elsewhere),
dropping market settlement and streaming usage capture.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>