Reuse SSH for WebCRT SFTP and fix folder navigation UX.

Open SFTP on the live session transport after SSH connect, pass the target path on every list refresh, and use folder/file icons in the browser panel.

Co-authored-by: Cursor <cursoragent@cursor.com>

web/src/services/api.ts

@@ -503,6 +503,8 @@ export type WebcrtSessionCreateResult = {
   state?: string;
   /** True when session used a vendor CLI hop (nested stelnet/telnet). */
   cli_hop?: boolean;
+  /** True when SFTP channel opened on the same SSH transport. */
+  sftp_ready?: boolean;
 };
 
 export const createWebcrtSession = (body: {