## Context
Adds an intellisense toggle for explorer notebooks similar to SQL editor
+ have QueryEditor render definitions via `useAddDefinition`
<img width="259" height="162" alt="image"
src="https://github.com/user-attachments/assets/278fdabd-1a24-4769-972e-1bce29060463"
/>
So intellisense will be running in the QueryEditor if intellisense is
enabled + source selected is database, otherwise will not run.
<img width="982" height="411" alt="image"
src="https://github.com/user-attachments/assets/19497aa0-36fc-49ab-853d-cb938b5b18e7"
/>
Also updated `useAddDefinition` logic to flush the table columns +
functions cache in react query
- For context in the past we had users run into browser performance
issues when definitions were loaded if their database is really big
- Hence why we originally added this intellisense toggle
- But we previously also required users to refresh the browser after
disabling intellisense, as a manual way to flush the cache
- So this change should remove the need to refresh the browser after
disabling intellisense
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **New Features**
* Added PostgreSQL IntelliSense with definitions, formatting, and code
completions in SQL editors.
* Added a notebook option to enable or disable IntelliSense, with the
preference saved between sessions.
* Improved the notebook’s empty-state appearance.
* **Bug Fixes**
* Improved IntelliSense cleanup and prevented duplicate registrations
when disabled.
* Improved query execution state handling while background IntelliSense
data loads.
* **Tests**
* Added coverage for shared registration, cleanup, preference
persistence, and IntelliSense-related query handling.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
