feat: migrate Channel manager UI to public contracts

[NWYLZW]

The Channel product renderer and Simulator adapter were maintained inside CordisX Host, which made plugin UI and service changes collide with Host work. This moves that ownership into the standalone Channel repository while keeping Manager chrome, credential capture, official credential-bearing adapters, persistence, transport, and the Channel runtime Host-owned.

The package contains the renderer, owned CSS, package/runtime manifest v8, and a Node service that registers only the exact manifest-authorized Simulator target through public ctx.channel. It reads the Host-stamped service configuration revision and cannot self-report a lower or higher revision. It imports no Host-private renderer, launcher, service-config, credential, path, DOM, or transport implementation.

Exact formal baselines:

• Protocol 3f0dbcd8b04ae83c920d2d913ac2c313af5f83f1
• Host dfb071e02eca0ef52f84d67b2393c25aced7d3f0

Validation:

• npm run check
• 16/16 artifact, public-boundary, model, authority, package, style, and service tests
• AJV validation of package/runtime manifests and exact digest
• built renderer/service artifacts

This PR establishes the independent plugin package. Deleting the old Host consumer and changing the Host default resolver to this exact package are a following Host owner change; until that lands, this merge alone is not the completed migration or user acceptance.

No live Codex Desktop launch or user acceptance was performed.