feat: null features in tag schema + add name filter to listRepositoryTags

[dankolafa]

This PR makes the repository tag tools usable against real Docker Hub data. Two related changes:

1. Fix: accept features: null in the tag image schema

listRepositoryTags and getRepositoryTag fail with an MCP output-schema validation error (-32602) for any repository whose tag images have features: null — a value Docker Hub commonly returns (for example, private organization images). Because validation runs against the whole response, the tools return no data at all.

The cause: RepositoryTag.images[].features was declared as a required, non-nullable z.string(), while every sibling field that can be empty (os, os_features, os_version, variant, digest) is already .nullable(). When Docker Hub returns null, the SDK throws:

Expected string, received null   (path: images[i].features)

This makes features .nullable() to match the Docker Hub API and the surrounding fields.

2. Feature: add an optional name substring filter to listRepositoryTags

Docker Hub's tags API supports server-side substring filtering via ?name=, but the tool never forwarded it — so there was no way to resolve a partial tag (such as a short git SHA) to its full tag. This threads an optional name parameter through, mirroring the existing architecture / os filters.

listRepositoryTags(namespace=…, repository=…, name="8f5ce31")
  → returns the full tag  8f5ce311d8d1ec01f6505801255c3810a239248a

tools.json is regenerated for both changes.

Note: the null-features fix is distinct from #71 (which was about pagination parameters). That one returned wrong/partial data; this one returned nothing at all for affected repositories.

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Tested on a local build against a live organization and its repositories.

[dankolafa]

@lucadruda @vdamery can anyone please take a look? Tagged you as two of the people who seem to review PRs around here 🙏