fix: make RDP drive redirection writable on the stock deployment (#1333)

* fix: make RDP drive redirection writable on the stock deployment

The default drive-path was /drive on the guacd side, which the official
guacd image cannot create as its non-root user, so every upload was
refused with guacd's raw "FAIL (CANNOT OPEN)" ack. Default to
GUACD_DRIVE_PATH (set to the shared termix-data volume in compose) with
one folder per user, and explain guacd's refusal in the file browser.

* style: format RDP drive settings

src/ui/locales/en.json

@@ -1952,6 +1952,7 @@
       "uploadFailed": "Failed to upload {{name}}",
       "uploadDisabled": "Uploads are disabled for this connection",
       "driveUnavailable": "Enable RDP drive redirection before uploading files",
+      "driveNotWritable": "guacd cannot write to the drive folder. Check GUACD_DRIVE_PATH (or the host's Drive Path) and its permissions.",
       "dropToUpload": "Drop files to upload"
     },
     "toolbar": {