feat(native): a link shared to TREK can go to the trip's links

A page or a link shared from another app now carries its address. The app asks whether to keep it among the trip's links (Collab, Links) or to read a booking from it. A link whose page the phone cannot read is no longer refused: it is handed over as the link alone, which can be kept. With Collab off a page is read as a booking, as before.

client/src/native/trekShell.ts

@@ -163,6 +163,10 @@ export interface SharedFilePayload {
   data: string;
   /** Set when the share sheet already asked which trip it belongs to (feature shareSheet). */
   tripId?: number;
+  /** The http(s) address of a shared page or link, which can go to the trip's links instead. */
+  url?: string;
+  /** The page's title, for that link. */
+  title?: string;
 }
 
 /**