Polish header and right-panel state controls

[cjdyer]

This PR improves the top-level editor UX by making the header feel more intentional and the side-panel modes easier to understand at a glance.

Changes:

• Replace the plain SwimDSL text chip with app header
• Restyle the app bar to give the header a stronger visual identity
• Make the File control read more clearly as a menu button with icon, hover, and open-state feedback
• Close the file menu when an action is selected for smoother interaction
• Redesign the right-panel switcher from icon-only disabled buttons to labeled controls with active-state styling
• Add a compact current-state summary for the right panel so users can immediately see what is open

Result:

• The header feels more polished and easier to scan
• The File entry point is more obviously interactive
• The render/tutorial/XML/hidden states are much easier to distinguish

[cjdyer]

Before:

After:

[hazzery]

@morganlee-dev, mr cjdyer here is my mate and decided he wanted to contribute with his slop cannon (codex). I personally don't like the gradient here, but would like to hear your thoughts on this change. The existing UI definitely isn't very special.

[morganlee-dev]

I agree on the gradient, I think it would probably look better with a single colour, I like blue on the right a bit better, but if we are trying to move away from the unspecial existing UI another colour would be better.
I think the new file button is an improvement , however I personally like the simplicity of the existing UI buttons for the right panel but from a UX view, having the button name instead of a tooltip is probably a smarter move.

One idea for the header is that it could be a swimming pool texture, in the spirit of swimDSL being a swimming program editor. Something in this direction for example: