fix: eliminate Rich live table flicker during ade run

[clkao]

Summary

• Replace Rich Live auto-refresh timer with manual debounced refresh to eliminate table flicker during ade run
• Table only redraws when data actually changes, at most every 200ms — zero redraws during idle periods
• Remove time.sleep(0.5) initialization delay that was only needed for the background timer

Approach

The RichTaskLogger previously used Live(refresh_per_second=4) which redraws the entire table by erasing and reprinting on every tick, even when no data changed. This caused visible flicker.

Now uses auto_refresh=False with _live.refresh() called manually from update_task_from_dict(), debounced to 200ms intervals. All refresh() calls happen outside self._lock to avoid deadlock (since refresh() → _create_table() → acquires the same lock). A final refresh() in stop() ensures the last state is displayed.

Test plan

• Run ade run with multiple concurrent tasks and verify table no longer flickers
• Verify task status updates still appear promptly
• Verify SYSTEM log messages still print above the table
• Verify table shows final state when run completes

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