feat: align Script Editor UI with PJ3 — layout, texts and widgets

Restructure the Reactive Script Editor dialog to match PlotJuggler 3:
description label on top; "Script Editor" / "Function Library" tabs; left
column with global code + function editor; right column with Name/Save +
Active Scripts + Recent scripts; borders on text boxes and lists.

- Active Scripts are in-memory (empty on restart); Recent scripts persist.
- The Function Library is a single editable Lua helper block with a validity
  semaphore and Apply / Restore-default actions.
- Double-click on an Active or Recent entry loads that snippet into the editor.

Author: pabloinigoblasco