feat(content): clarify page and collection creation - #5592

Content’s plus button used to create a page immediately, even when the user wanted a collection. The editor’s earlier type chooser also disappeared after a title was entered. This PR makes the object type an explicit choice while keeping page writing fast.

• The top-level plus opens Page and Collection in both expanded and collapsed sidebar states. Escape closes the menu without creating anything.
• Creating a Page or Collection from a different workspace row waits for workspace selection before creation and holds that choice explicit until the new route opens; the same sequencing covers child creation.
• The workspace-name dropdown switches spaces and offers New workspace and Local folder. Opening the new-workspace dialog waits for the menu to close so the name field receives focus.
• An empty page keeps a Create collection starter after title edits. The starter waits until collaborative editing is ready; conversion saves the current title and body and preserves the latest stored description.
• /database offers inline and full-page collections. Full-page insertion replaces its containing paragraph as a block, matching /page, and uses a stable document ID/idempotency key so a lost response can be retried without a duplicate. Inline collection and slash Page creation allocate document IDs before calling their actions, allowing cleanup even when a creation response is lost; inline creation also supplies its block ID. All slash Page/Collection creation paths remove a newly inserted reference and use a creator-scoped rollback action if saving the parent fails; the action refuses to trash a linked or changed resource and distinguishes an absent resource from one it moved to Trash. Both collection paths use collection-neutral success feedback in every locale.

No schema changes are involved. During final CI, a security guard found an unscoped cache update in Slides inherited from main; the update now requires editor access in its SQL predicate. Viewer reads still return the design system, but no longer write that cache field.

Validation

• Focused editor, sidebar, database, rollback, and hook tests: 185/185 passed. A database-backed test verified caller-supplied inline IDs, creator-scoped rollback, and absent-resource reporting (27/27 in that file); focused slash Page creation tests passed 41/41 after the final repair. Content typecheck passed. Parity matrix and rollback tests passed 7/7. Slides' focused design-system tests (3) and typecheck passed after the main merge. Local production-credential diagnostics are expected in this dev environment.
• CI passed on the merged-with-main head, including all five targeted fast-test lanes and required checks.
• Human QA on earlier heads covered expanded and collapsed creation menus, Escape, root Page and Collection creation, workspace/source menu, workspace dialog, and titled empty Page conversion. On this head, a new Page received an inline /database collection; its table persisted after reload. A separate /page command created a child Page and retained the parent reference after reload. The browser reported no errors. On the preceding head, the full-page /database flow created one collection, opened its table, and retained the parent reference after reload with no browser console or network errors. Disposable QA pages and their children were moved to Trash. The lost-response cleanup paths are covered by focused database and hook tests; a real network response-loss simulation has not been run.

content_product_impact:
  lane: contract_repair
  features:
    - content.feature.durable-foundations
  capabilities:
    - content.object.page
    - content.object.database
    - content.agent.action-parity
  record_change: none
  proof:
    - corepack pnpm --filter content exec vitest --run app/components/sidebar/DocumentSidebar.layout.test.ts app/components/editor/SlashCommandMenu.test.ts
    - human QA through Content's creation and conversion flows
  rationale: The change repairs object creation choice and conversion without changing the accepted Page or Database contracts.