B3 — Establish the feature-pack contract (frontend extension point)

[KrasForge]

Part of EPIC B0 #293

Depends on: B1 #294
Blocks: B7

Context

Mirror the node-pack model on the frontend so a pack can contribute views, editors, commands, and routes against ModuloCoreAPI under declared capabilities — the same mechanism the note experience will then conform to.

Scope — in

• FeaturePack descriptor + registerFeature(...) registry with lifecycle (register → mount → unmount) and capability declaration.
• Contribution points: routes, views, editor surfaces, commands.
• One trivial built-in feature registered through it to prove the path end-to-end.

Scope — out

• No marketplace/distribution work (packs are in-repo for now).

Acceptance

• Registry + lifecycle implemented; capabilities declared per pack.
• A hello-world feature mounts/unmounts via the contract with the app otherwise unchanged.