Vrl Playground Ux.Enhancement

Improved the VRL playground UX:

• Added resizable panels via draggable gutters.
• Added a dark/light/system theme toggle that syncs with the OS preference.
• Added run history persisted in localStorage, with a clear button.
• Added a Shift+Enter shortcut to run the program.
• The Share button now copies the shareable URL to the clipboard.
• Various visual polish (unified header, purple accents, tightened spacing).

authors: pront