Copilot welcome screen and pasted job descriptions

What changed

• A new Copilot chat now opens with a heading and the message box centered on the page. Navigation menus now say Recruiting Copilot, Educator Copilot, or Student Copilot where they used to say Agent.
• A job description pasted on its own into Recruiting Copilot now gets a full proposed assessment in the reply, with no other instructions needed. Reused library questions on a proposal can be expanded to read the full problem statement.
• In course labs, the button that moves you to the next step stays locked until Rena has marked the current one. The step arrows are for reading ahead and do not change your progress.