fix(registry): preserve published pet manifests

[JPJeePee]

Root cause

The 0.2.2 Pet Studio release added pet.custom.manage by tightening the existing convax.plugin/5 Pet rule from three capabilities to four. Registry Pages revalidates every immutable published Release, so the valid 0.2.1 entry was rejected before the new catalog could be rebuilt.

Fix

• keep the three activity/preference capabilities required for every Pet Plugin
• allow the exact pet.custom.manage capability as the only optional fourth Pet grant
• keep unrelated capabilities and executable runtimes rejected
• update the v5 JSON schema and public authoring/Registry docs
• advance Registry sequence to 32

Regression coverage

• added a test that failed against the published 0.2.1 capability set before the fix
• verified the actual published plugin-convax-pet-v0.2.1/registry-entry.json parses with the repaired validator
• bun run check passes: all workspace builds, typechecks, tests, companion builds, validation, deterministic packing, Registry, and Showcase generation