In-app editor P1 — extract editor panes into a shared package

[mabry1985]

Lift the live editor's panes into a reusable package so the app can use them (plan: docs/internal/inapp-editor-parity.md).

• New packages/editor-ui (name TBD): ShaderPane / ControlsPane / BindingsPane / MetaPane / JsonPane as controlled, stateless components — take an OrbDefinition + callbacks, use @orbis/orb-runtime (compileCheck/validateOrbDefinition/buildFragmentSource).
• Refactor sites/editor to consume them with zero UX change (proves the extraction is clean).

Depends on nothing; unblocks P2.

[mabry1985]

Parked: extraction is done on branch feat/editor-ui-package but PR #553 was closed (no in-app consumer yet — we route to the marketing editor via #554). Revive the branch when building the in-app editor.