New: Add access widget for _access sharing (fixes #486)

[taylortom]

Fixes #486

New

• Add an Access backbone-forms editor (app/modules/scaffold/views/scaffoldAccessView.js) that renders one exclusive-tier sharing control over the flat _access object, replacing the legacy _isShared / _shareWithUsers fields:
  • Only me → { public: false }
  • Specific people → { public: false, users: [...] } (Selectize people picker over GET api/users, reusing the existing scaffoldUsersOption template)
  • Anyone → { public: true } (clear-on-public: the in-memory people list is cleared; nothing is auto-saved)
• Unknown _access keys are preserved on save.
• Tier labels added to app/modules/scaffold/lang/en.json (app.scaffold.access.*).
• Scope is public + share-with-users only — user groups (_access.groups) are intentionally out of scope for this UI.

Update

• app/modules/scaffold/index.js getType now honours the canonical schema annotation _adapt.inputType (in addition to the legacy _backboneForms) when resolving an editor. The _access field is expected to carry _adapt.inputType: "Access" in its served schema — the UI does not force a _backboneForms type client-side.
• Legacy _isShared / _shareWithUsers are hidden via ATTRIBUTE_BLACKLIST so they don't render alongside the widget during the cutover (the fields stay in the DB, readable, until the later contract step).
• Read-side now reads _access instead of the legacy fields: courseModel.isEditable (app/core/models/courseModel.js) and the shared-project delete prompt (app/modules/projects/views/projectView.js).

Testing

• npx standard — passes (app/ is excluded from the standard config; all editor changes live there).
• npm test — 60/60 pass (the suite covers the Node build/lib layer, which is untouched).
• The editor seeds tolerantly from the legacy _isShared / _shareWithUsers fields when _access is absent, so it works before and after the backfill migration.
• Release-gated / not yet end-to-end testable. This is part of the api#98 step-3 clean cutover: _access only appears in the course schema once the enforcement chain lands (New: Extend _access with users key adapt-authoring-users#46 _access.users, New: Enable access control adapt-authoring-content#117 opt-in, Update: Remove checkContentAccess in favour of generic _access adapt-authoring-adaptframework#194 remove legacy paths + backfill). Do not merge/deploy ahead of that chain or sharing toggles will write a field nothing reads.

Depends on (schema)

• The served _access schema must annotate the field with _adapt.inputType: "Access" (and ideally a title/description for the section heading and help text). This is the schema-side counterpart to the getType change above and should land with the cutover.