marketplace: entries declare a pinned version but source ref: main — the declared version does not pin bytes

## Why

**Why this is worth a look:** the `vsdd-factory` entry declares `"version": "1.0.0-rc.24"` and sources `"ref": "main"`. Today those agree — `main` and the `v1.0.0-rc.24` tag are both `89f6f87cf476b1f57d979962eabf0d9b20a49e69` — so anyone installing right now gets exactly what the version string promises. The moment `main` moves ahead of the tag, that same declared version starts resolving to different bytes, with no version change to signal it.

**Why it might still be worth changing:** the version string is the only handle a consumer has. Anyone who archives, re-verifies, or reproduces plugin bytes from the declared version cannot treat it as a pin. We build signed, reproducible bundles from upstream sources, so we record the commit SHA instead — but that is a workaround for something the manifest could state directly.

## What we see

```console
$ gh api repos/drbothen/claude-mp/contents/.claude-plugin/marketplace.json --jq '.content' \
| base64 -d | jq '.plugins[] | {name, version, ref: .source.ref}'
{ "name": "vsdd-factory", "version": "1.0.0-rc.24", "ref": "main" }
{ "name": "secops-factory", "version": "0.9.0", "ref": "main" }
```

Both entries use `ref: main`, so I take this to be deliberate — `main` as the release branch, version as a label for what currently sits there. If that is the intent, please close this; the behavior is consistent and the tags are there for anyone who wants to pin by hand.

If it is not the intent, pointing `ref` at the release tag would make the declared version mean the bytes it names, at no cost to the rolling-`main` workflow.

Small thing, and only surfaced because we consume the manifest programmatically. Thanks for publishing these.