Word validation errors from the catalog too

[arav-agarwal2]

Pydantic validation failures reached the report as Pydantic's own text: its built-in messages ("Field required"), and our validators' hand-written ValueErrors behind a "Value error," prefix, located at "(top level)" when a model-level validator failed. None of it was in the catalog.

• Validators raise messages.Invalid(rule, key, **values), a ValueError rendered from the catalog; the loaders report it at the field that failed, keeping its fix and spec. compute_regions raises it too.
• A _pydantic catalog section words Pydantic's built-in errors by error type, using the error's context values and {input}.
• Tests: Invalid calls are checked like err() calls; no bare ValueError may be raised under models/; the _pydantic entries must match exactly the error types the file models' schemas can produce; and bad files through each loader render entirely from the catalog in strict mode.

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