fix: Electron title bar hidden under macOS traffic light icons (#647)
The responsive CSS breakpoints at 768px and 480px used the `padding`
shorthand on `.app-topbar`, which reset `padding-left` to the compact
value and clobbered the electron-specific `padding-left: 96px`.
Fix: add `.is-electron .app-topbar { padding-left: 96px }` inside both
media queries to preserve traffic light clearance on narrow windows.
Also removed duplicate electron padding rule that was split across two
locations in the file (lines 1850 and 8759).
Closes #647