iOS: improve QR pairing flow (#51359)

- improve QR pairing UX and bootstrap token handling
- preserve repeated optimistic user messages during refresh
- add regression coverage for refresh reconciliation

Thanks @ImLukeF

src/plugins/commands.ts

@@ -322,7 +322,7 @@ function resolveBindingConversationFromCommand(params: {
   from?: string;
   to?: string;
   accountId?: string;
-  messageThreadId?: number;
+  messageThreadId?: string | number;
 }): {
   channel: string;
   accountId: string;

src/plugins/types.ts

@@ -963,7 +963,7 @@ export type PluginCommandContext = {
   /** Account id for multi-account channels */
   accountId?: string;
   /** Thread/topic id if available */
-  messageThreadId?: number;
+  messageThreadId?: string | number;
   requestConversationBinding: (
     params?: PluginConversationBindingRequestParams,
   ) => Promise<PluginConversationBindingRequestResult>;