[codex] Improve conversation timeline

[hanhan3344]

Summary

• Position conversation timeline markers from the actual scroll location of each user prompt instead of distributing them only by question order.
• Harden timeline tooltip rendering so long prompts stay inside the bubble and truncate cleanly.
• Reduce unnecessary timeline rebuilds by using relevant mutation filtering and timeline signatures, while refreshing marker positions on resize.
• Add keyboard activation and tooltip ARIA wiring for timeline markers.
• Make the Windows installer test assert the actual configured Python executable so it passes outside Windows-specific Python paths.

Root Cause

The timeline tooltip had a max width but no overflow clipping, so long prompt summaries could draw outside the visible bubble. Marker placement also ignored real scroll positions, and the mutation scheduler was broad enough to rebuild the timeline for many unrelated DOM changes.

Validation

• node --check codex_session_delete/inject/renderer-inject.js
• uv run --extra test python -m pytest -q

[BigPizzaV3]

干得漂亮