CatalogEntry.from_dict used `data.get("requires") or {}` and
`data.get("provides") or {}`, so a FALSY non-mapping ([], '', 0, false) was
coerced to {} before the isinstance guard — a corrupt catalog entry passed
silently. Only a truthy non-mapping was rejected.
Handle None explicitly and reject every other non-mapping, mirroring the
merged manifest requires/provides/integration guards (#3629, #3661).
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Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>