Add optional frameless Linux desktop windows

[salemsayed]

Summary

• add a Linux-only --no-window-frame startup option
• keep the native Electron frame as the default
• document the option for window managers that provide their own controls
• cover argument resolution and BrowserWindow construction

Why

Tiling Wayland compositors such as Hyprland already provide window movement,
resizing, borders, and close controls. Electron's native Linux menu/title bar
duplicates that chrome and consumes vertical space. This opt-in mode lets those
users rely on their window manager without changing the default experience for
other Linux desktops.

The option is startup-only because Electron chooses frame when constructing a
BrowserWindow. macOS and Windows ignore the Linux-only flag.

Screenshots

Before — native Linux frame:

After — --no-window-frame:

Validation

• pnpm --filter @bb/desktop test — 34 files, 217 tests passed
• pnpm --filter @bb/desktop typecheck
• focused Prettier and git diff --check
• built bb-0.38.0-x86_64.AppImage
• launched native-frame and frameless AppImages side by side on Hyprland with isolated data and ports
• verified the frameless native Wayland window, server health, and host-daemon listener