fix: enable DWS WebSocket in dev mode without code changes

Relates to issue #571298 (closed)

_This MR was created by Duo in _Session 1129315

Changes

• Modify WebSocket upgrader in Duo Workflow handler to respect development mode
• Remove need for manual code changes when testing Agentic Chat in Web UI
• Update documentation to reflect the improved development experience

How to validate

1. Check out this branch
2. cd workhorse && make && gdk restart gitlab-workhorse
3. Confirm that Agentic Duo Chat works in the web

Before this change:

After this change: