## Summary
- Adds a close button to the "Introducing unified logs" sidebar banner,
storing the dismissal in localStorage so it stays hidden.
## Test plan
- [ ] Open Logs Explorer, confirm the X dismisses the banner and it
stays gone after reload.
<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit
* **New Features**
* Added an `X` close button to the unified logs preview banner.
* Remember banner dismissal using local storage, so it stays hidden
after closing.
* Updated banner visibility rules to account for unified-logs preview
enablement and default opt-in state.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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Co-authored-by: Joshen Lim <joshenlimek@gmail.com>