Changes:
- Add DEFAULT_WAIT_SECONDS = 50 (replaces config.default_wait_seconds)
- Add DEFAULT_EMPTY_RESPONSE = 'call this tool... ' (replaces config.default_empty_response)
- Remove wait and empty response fields from WebUI Settings panel
(only agent_stale_after_seconds remains configurable)
Rationale:
These values are fundamental to the 60s timeout mitigation strategy and
should not be user-configurable. The 50s wait with 5s keepalives is the
optimal balance for staying under the Copilot 60s wall-clock limit while
providing responsive progress feedback.
