Implements fixes from issue #1880 and #1934 to prevent exit code 130 timeout in CI environments:
- Add lastEventTimestamp to EventState for tracking when events were last received
- Add event watchdog: if no events for 30s, verify session status via direct API call
- Add secondary timeout: after 60s without meaningful work events, check for active children/todos and assume work is in progress
This prevents the poll loop from waiting for full 600s timeout when:
1. Event stream drops silently (common in CI with network instability)
2. Main session delegates to children without producing meaningful work on main session
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