feat(plugin): publish Convax Pet

[JPJeePee]

Summary

• publish Convax Pet as a real convax.plugin/5 Pet feature Plugin
• add the transport-neutral v5 Pet manifest contract and convax.pet-host/1 boundary
• ship the local Violet atlas, overlay, settings, preferences, activity mapping, and lifecycle behavior
• keep the package static and sandboxed, with no executable runtime and no legacy Goku format compatibility
• document, validate, pack, and index the Pet contribution at Registry sequence 30

Release

• tag: plugin-convax-pet-v0.2.1
• artifact: convax-plugin-convax-pet-0.2.1.zip

Verification

• bun install --frozen-lockfile --ignore-scripts
• bun run check
• bun tooling/pack.mjs --tag plugin-convax-pet-v0.2.1
• focused v5/Registry/workspace tests: 37 passed
• Pet workspace tests: 23 passed