## Context
More groundwork for the Explorer - this one's focused on initializing
the valtio store for managing notebooks
Store architecture will follow closely with the existing
sql-editor-store
No data persistence yet, but can test creating a new notebook
<img width="195" height="143" alt="image"
src="https://github.com/user-attachments/assets/8656fb5b-3a8e-4f71-b2ce-d2f34ca9b552"
/>
Which should open a placeholder page
<img width="1387" height="527" alt="image"
src="https://github.com/user-attachments/assets/4a81b1ae-a740-40e6-9d33-29fa4f83b541"
/>
Closing the notebook brings you back to the explorer home page
<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit
* **New Features**
* Added support for creating and opening project notebooks from the
Explorer.
* Added notebook tabs alongside existing entity and SQL tabs.
* Added notebook management, including loading, renaming, removing,
editing cells, and tracking unsaved changes.
* Added support for SQL, logs, and Markdown notebook cells.
* Added dedicated notebook routes and an initial notebook editor view.
* Added notebook icons throughout the Explorer interface.
* **Documentation**
* Documented session-scoped notebook state for query results and row
limits.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
