Add utility title bar and restore editing shortcuts

[w-ade]

Summary

• Switch Visto from a borderless custom chrome window to a standard macOS utility panel (NSPanel + .utilityWindow) with the system title bar and traffic lights.
• Remove the hand-rolled close/minimize/zoom buttons from the address strip; keep URL field + reload below the title bar.
• Keep first-responder handling on the web view so Delete / Command-C/V work in page inputs and the address field.

Why

Borderless windows do not become key by default, which blocked normal editing keys. A utility title bar also matches the compact chrome expected from small Mac tool apps.

Test plan

• Build and launch with ./script/build_and_run.sh
• Confirm the window shows a utility-style title bar with traffic lights and “Visto”
• Click the address field: Delete, Command-C, Command-V, typing all work
• Focus a text input in a loaded page and verify the same shortcuts
• Command-W closes; File > New Window still works