Feature/wiki prevent ancestor reversion milkdown

[NishikawaKoharu]

Purpose

Prevent wiki "ancestor reversion": closing the editor left IndexedDB drafts that could overwrite newer content when reopening and saving. Improve close / re-edit behavior for both single-user and collaborative editing, while preserving expected Preview and collaborator-name behavior.

Changes

• Show an unsaved-changes confirmation only when closing with local unsaved edits (single editor)
• On Close / Discard / Save and Close, clear the local IndexedDB draft cache
• Keep the y-websocket connection and Y.Doc alive on Close (do not tear down the shared collaborative session)
• On re-edit, recreate the tab's local session when needed and use awareness to decide live collab state vs. latest DB content
• During collaborative editing, skip the close confirmation (showing "Discard" would be misleading)
• During collaborative Close, keep Wiki version on Preview and keep the editor instance (leaveCollaborativeEditMode)
• Clear awareness on collaborative Close, and restore the local user name on re-edit via setLocalAwarenessUser (works after setLocalState(null))
• Use disableBc: true to avoid BroadcastChannel-related issues across tabs
• Suppress the beforeunload warning after intentional Save and Close navigation
• Fix focus when entering edit mode on a newly created wiki page

Companion UI/i18n PR: RDM-osf.io (edit.mako, messages.po).

QA Notes

• Does this change require a data migration? If so, what data will we migrate?
  • No
• What is the level of risk?
  • Medium (editor close/re-edit and collaborative awareness paths)
• Any permissions code touched?
  • No
• Is this an additive or subtractive change, other?
  • Behavioral change to wiki editor close / re-edit / draft-cache handling
• How can QA verify? (Through UI, API, AdminApp or AdminAdminApp?)
  • Through UI (with the RDM-osf.io companion PR deployed):
    1. Single editor, unsaved changes: Close → confirmation modal → Discard or Save and Close
    2. Single editor, no changes: Close → no modal, editor closes
    3. Stale draft prevention: Edit → Close (Discard) → another user/session updates and saves → reopen edit → content should reflect the latest saved version, not the discarded draft
    4. Collaborative editing Close: Two users/tabs editing the same page → Close on one side → no confirmation modal; Wiki version stays Preview; the other editor continues
    5. Collaborative re-edit: After Close, re-enter Edit → the other side shows this user's name again
    6. Re-edit after Close: Content / collab state are correct
    7. Save and Close: No unexpected beforeunload browser warning
• If verifying through API, what's the new version? Please include the endpoints in PR notes or Dev docs.
  • N/A
• What features or workflows might this change impact?
  • Wiki Milkdown editor: Close, Discard, Save and Close, re-edit, collaborative editing, collaborator name display
• How will this impact performance?
  • Minimal; short awareness settle wait on editor load / re-edit only

Documentation

• No documentation updates required

Side Effects

• IndexedDB drafts are cleared on Close / Discard / Save and Close (intentional)
• Close no longer destroys the shared y-websocket / Y.Doc session for other collaborators
• During collaborative editing, Close skips the unsaved-changes dialog and keeps Preview
• During collaborative Close, the local user disappears from awareness until they re-enter Edit

Ticket

https://redmine.devops.rcos.nii.ac.jp/issues/61563