Align Core namespaces and builder extension typing

[woksin]

Arc for TypeScript 0.24.0 continues aligning @cratis/arc.core with Arc.Core's namespaces and cleans up its public surface. None of these packages has been published to npm. npm publication remains disabled, and full .NET parity is not yet available.

Added

• server.validateCommand(...) and app.validate(...) run a command's authorization and validation without executing it, like .NET's command pipeline Validate.

Changed

• Builder methods added by integration packages (withChronicle, withMongoDB, withDrizzle, addCratis) are typed through a builder extension interface, so they type-check wherever the builder is used, including in @cratis/arc.testing and in installed packages.
• Core modules live in the namespaces that own them, as in Arc.Core.

Removed

• The validateOnly flag on executeCommand and execute; use validateCommand and validate.
• Internal result helpers (malformed, status, emptyPaging, commandResult) from the root export; recordFailure moved to @cratis/arc.core/hosting.

Fixed

• A clean build of the repository no longer fails on the Chronicle testing scenario's builder typing.