* docs: reference kandev-plugin-template starter repo in plugin guides
Link the new kdlbs/kandev-plugin-template repo from the authoring guide as the
recommended "Use this template" starting point, and from the marketplace guide's
release step. Clarify the two release assets: the in-tar checksums.txt verified
on install versus the release-level checksums.txt (tarball digest) pinned as the
catalog's package_sha256.
* docs: describe package_sha256 as advisory, not yet index-pinned
* docs: mark release checksums.txt asset as optional for consistency
* docs: mark checksums.txt optional in marketplace submission step too
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Co-authored-by: Kandev Agent <agent@kandev.dev>
João Salavisa
948b3b62d0