adding a worktree switch feature

apps/app/src/lib/http-api-client.ts

@@ -699,13 +699,15 @@ export class HttpApiClient implements ElectronAPI {
       sessionId: string,
       message: string,
       workingDirectory?: string,
-      imagePaths?: string[]
+      imagePaths?: string[],
+      model?: string
     ): Promise<{ success: boolean; error?: string }> =>
       this.post("/api/agent/send", {
         sessionId,
         message,
         workingDirectory,
         imagePaths,
+        model,
       }),
 
     getHistory: (