Remove a few unused strings for localization

#7949)

Code changes responding to the PR review:

- Team Collections (review #1/#3/#4/#13): BloomBridge's mutating external
  endpoints (add/update/process-book) now fail fast on a Team Collection rather
  than silently corrupting a shared collection (they don't honor checkout, the
  TeamCollection.status file, or TC renames). Adds
  CollectionModel.IsEditableCollectionATeamCollection and
  ExternalApi.RefuseIfTeamCollection, and documents the non-TC assumption on
  CollectionModel.AddBookFromFolder.

- Off-screen JS bridge cleanup (#6/#7/#8) in BookProcessor: the capture trigger
  is now fire-and-forget (its result was discarded), the redundant
  Application.DoEvents() in the poll loop is removed (the sync call already pumps
  the loop), and WaitForJavascriptResult documents why the off-screen processor
  keeps the poll-a-window-global approach rather than the live editor's async
  API callback.

- Async page-readiness (#10/#11/#15): SetImageDisplaySizeIfCalledFor now
  registers a requestPageContent delay around its asynchronous image-info fetch
  and resize, so captureContentForExternalProcessing waits for image sizing to
  finish before capturing. Corrects the editablePage.ts comments that wrongly
  called the load-time fix-ups "synchronous", and clarifies the natural-size
  fallback in autoFitImageOverTextSplits.

- autoFit overlays (#14): fitOneImageOverTextSplit now also skips pages whose top
  pane has non-text overlays (canvas elements other than the background image),
  not just text overlays.

- Smaller comment fixes: clarify the "already in the collection" guard in
  AddBookFromFolder (#2); document that the process-book overlay message is
  intentionally not localized (#12); note that priorForeground is captured once
  on purpose (#5); move the JSON-vs-delimiter note next to the code it describes
  (#16); raise the ExternalBusyOverlay z-index (#17).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>