Extends `dispatchKindEntry` in `runtime-artifact-layout.cts` to route
agents-kind entries through a converter when the descriptor carries a
non-null `converter` field. Adds `stageAgentsForRuntimeWithConverter`
to `install-profiles.cts`, expands `VALID_CONVERTER_NAMES` with the 9
agent converter names, and adds a fail-first behavioral test suite
(9 tests) proving the new wiring end-to-end.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
