v0.1.6-dev.4: default forward Host compatibility

Newer DSH releases remain eligible without republishing the plugin for each RC. Host admission now uses engines.dsh >=0.2.0-rc.2, with matching DSH peer ranges and compatibility metadata. The known minimum is retained; add an upper bound or exclusion only for a confirmed incompatibility.

Build SDK inputs stay pinned to 0.2.1-rc.1; an admitted Host version is not a claim that every future version has been runtime-tested. No feature or permission behavior changed.

Validation: 155 source tests passed, including forward-admission and minimum-version regression tests. Applicable type checks, builds and package-contract checks passed.