fix: fail closed for Compose assets, then track jQuery removal

[chubes4]

Immediate bug

The Studio render and REST gates fail closed when ec_is_team_member() is unavailable, but some asset/editor conditions still use:

function_exists( 'ec_is_team_member' ) && ! ec_is_team_member()

That shape does not deny access when the helper is missing. As a result, editor dependencies or jQuery preservation may run for logged-in non-team users even though the Studio app itself does not render.

Relevant files:

• inc/assets.php
• inc/compose-editor.php
• src/blocks/studio/render.php as the correct fail-closed reference

Immediate acceptance criteria

• Every Studio asset/editor gate allows administrators or a present helper returning true.
• Missing team helper denies all non-administrator Studio assets and editor setup.
• Tests/source contracts cover logged out, administrator, team, non-team, and missing-helper states.

Long-term tracking

Studio currently preserves jQuery while Compose is active because the Blocks Everywhere/editor stack requires it.

Remove that compatibility behavior only after verifying the current upstream editor dependency no longer needs jQuery. Do not replace it with Studio-specific editor bootstrap code.