Add option to enable line numbers by default in text labeling interface

**Is your feature request related to a problem? Please describe.**

When labeling long texts, I often need line numbers visible for reference. Currently, users must manually enable “Show line numbers” in the interface settings each session, which is repetitive.

**Describe the solution you'd like**

Provide a project-level or global setting to have line numbers enabled by default, so all annotators see them without needing to toggle manually.

**Describe alternatives you've considered**

Adding instructions for annotators to enable line numbers manually (not reliable).

Injecting custom scripts to force the toggle (hacky and unsupported).

**Additional context**