fix(desktop): integrate macOS titlebar controls

[tonyfettes]

Summary

• use Proton's titlebar overlay on macOS so SeekMoon paints the native window-control area
• reserve and align the traffic lights in both packaged and development HTML entries with a 36px header and an 80px leading inset
• add a packaging regression test for the native platform marker while leaving the browser console unchanged

Validation

• moon -C desktop check . --target native (passes with 54 existing warnings)
• moon -C desktop check frontend --target js (passes with 70 existing warnings)
• moon -C desktop test package/internal/packaging --target native (16/16 passed)
• moon -C desktop info
• moon -C desktop fmt
• git diff --check
• visually verified through user-provided macOS development screenshots

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Reserve traffic-light space for the narrow file panel

When a macOS window is resized to 760px or narrower and the file panel is opened, responsive.css makes every .content.panel-open .editor fixed at inset: 0 and hides the expand control, while this inset only applies to the normally-false panel-expanded state. The first editor tabs therefore retain their 12px padding and render directly underneath the native traffic lights; apply the leading inset to the narrow full-screen panel-open state as well.

Useful? React with 👍 / 👎.

[tonyfettes]

This sometimes crashes the application on exit.