Migrate to new bidirectional references

[lveillard]

Migrate SurrealDB schema generation to use native bidirectional references.

This change replaces the custom event-based reverse propagation with SurrealDB's built-in REFERENCE and references<> types, simplifying schema management and aligning with the database's new capabilities.

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[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
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