Build a V3-native query engine

[em3s]

Background

v2.engine.Graph is a god class – early tech debt.
The V3 API path currently runs on V2Backed* adapters over V2 internals – a transitional shape.
This issue replaces the query path with a V3-native engine. Mutation is out of scope (do it later).

Task

• Engine skeleton – Empty Engine Spring bean with a catalog reload loop
• Catalog reload – Engine periodically loads databases / tables / aliases from the metastore via a CatalogLoader
• Query – Engine produces TableBinding instances; QueryService uses it

Done When

• V3 query controllers serve traffic through Engine instead of V2BackedTableBinding.
• Graph is unchanged.
• Each phase lands as one or more independently shippable PRs.

Notes

• "Catalog" = the registry of Database / Table / Alias definitions (Spark / Trino / Iceberg / Glue use the same term). The metastore stays as the Actionbase Table backing store; the catalog is what lives in memory and is loaded from the metastore.
• Reuse core.edge.mapper.*, core.edge.payload.*, core.metadata.common.* — these are already V3.

[em3s]

I'll handle the first task to establish the initial direction. After that, could you please take over the rest of the implementation? @zipdoki

[zipdoki]

@em3s
Sounds good! Feel free to ping here once the work is complete — happy to take a look.