W5: "Shared with me" documents (needs a backend route — A11) #54

Part of #44 · Lane W5 — documents · Size M · blocked on a backend route (ask A11)

Parity evidence — and a correction

work-consolidation.md records this as "not a gap — the web lacks it too". That is wrong.
The web ships it, server-rendered, which is why an endpoint diff missed it:

• app/documents/layout.tsx:21-29 → getSharedDocuments(user.id)
• components/documents/DocumentsWorkspace.tsx:44 → <SharedDocumentsList documents={…} />
• components/documents/SharedDocumentsList.tsx — a "Shared with me" panel with the owner and
  the viewer's role (Viewer / Editor / Admin).

iOS today

Views/DocumentsView.swift shows only documents the user owns. A document shared to an iOS
user is reachable only if someone hands them a share-link token. Lists already got their equivalent
(GET /api/lists/watching → "Shared with me" section, #40); documents have no equivalent route.

Blocking backend ask (A11)

Add GET /api/documents/shared-with-me (or GET /api/documents?scope=shared) returning the same
shape getSharedDocuments() already produces — { id, title, role, updatedAt, isPublic, owner } —
authorized with getCurrentUserOrSyncToken so Bearer clients can call it.

Tracked as A11 in #66. Do not work around it by walking every document's
collaborator list.

Build this (once the route exists)

• sharedDocuments() in APIClient+SharedDocuments.swift.
• A Shared with me section in DocumentsView, kept out of the owned-documents folder
  tree (same rule as AppDataStore.watchedLists — the tree nests within the owner's
  hierarchy, so foreign documents must not be inserted into it).
• Row shows owner handle + role badge; tapping opens the document read-only or editable
  according to role.
• Editing gates on role (watcher = read-only, collaborator/manager = editable) and the
  offline sync outbox must not queue writes for read-only documents.

Acceptance criteria

• A document shared to the account appears under "Shared with me" without a share link.
• Role is respected in the editor; read-only documents cannot enter the sync outbox.
• Owned-document folder tree is unchanged.
• Unit tests for the new call + the tree-exclusion rule.

Files: new Services/APIClient+SharedDocuments.swift, Services/AppDataStore.swift,
Views/DocumentsView.swift.