feature: OneDrive folder as a second send transport

send(anchor:) now branches on TransportSettings.transport(). OneDrive mode
skips AirDrop entirely: it verifies the resolved OneDrive folder exists right
before composing (never trusts stale state), archives the session immediately
after the PDF lands, and sets "Saved to OneDrive — N page(s). Open it in Files
on your iPad." AirDrop's existing behaviour, including handleDidFailToShareItems,
is untouched and only reached from the .airDrop branch.

AppModel seeds outbox/watch from TransportSettings.effectiveFolders() instead
of FolderSettings.resolve() directly, tracks the live `transport`, and
bootstrap() creates the OneDrive folder and sets the watcher's
recordUncommented flag (true only for AirDrop) before the watcher starts.

Settings gets a "Send via" segmented picker above Folders. AirDrop shows the
existing watch/output rows; OneDrive shows a single read-only OneDrive folder
row (Choose... reuses the existing directory picker) plus one caption
explaining the same-folder round trip, or a "No OneDrive folder found" prompt
when nothing resolves (Choose... stays usable). Switching transport re-points
the watcher's folder and recordUncommended live; AirDrop's own folder
overrides are stored separately and are untouched by a OneDrive-and-back
round trip.

Menu's "Send..." row reads "Send to OneDrive" when that transport is active.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012ZiTXPbPCSjzPVsfoweAbp

Sources/Shotdeck/MenuBarView.swift

@@ -91,7 +91,7 @@ struct MenuBarView: View {
                     model.setStatus("Send is not available in this build.")
                 }
             } label: {
-                actionLabel("Send…")
+                actionLabel(model.transport == .oneDrive ? "Send to OneDrive" : "Send…")
             }
             .disabled(model.session.isEmpty || model.isSending)