feat(desktop): add Ubuntu x64/arm64 DEB support and Linux desktop integration

[xhd0728]

Summary

• Build Ubuntu 22.04-based x64 and arm64 DEBs, publish architecture-specific update feeds, and include both packages in the daily release.
• Add Linux tray/background behavior, launcher/icon permission checks, update support, and a single-row title bar with native window controls.
• Render Linux application-menu popups from the current Electron menu template in the window so all five menus follow PilotDeck's language and light/dark preference without a distro-specific GTK theme override. Keep native menu accelerators registered.
• Run package, X11, Wayland, menu, language, theme, and updater checks for both architectures before merge and during daily builds.

Verification

• Desktop TypeScript compile and UI desktop/updater tests: 37 passed.
• Desktop Node tests: 89 passed, 1 skipped.
• Ubuntu 22.04 arm64 user space: rebuilt and installed DEB; launcher, icon, bundled native modules, packaged updater, and installed-app boot under X11 and Wayland passed.
• Ubuntu 22.04 arm64 X11 and Wayland interactive chrome smoke: menu actions, keyboard navigation, all five English/dark and Chinese/light menus, and live theme updates passed.
• YAML syntax and git diff --check passed.

Compatibility limits

Ubuntu 22.04 is the build baseline. The menu solution does not depend on GNOME, Yaru, or a particular GTK theme, but Kylin, Deepin, and UOS versions still need their own installation, tray, terminal, and updater checks before a specific release can be certified. Native x64 desktop results await the CI runner. A published Linux release is needed to test the complete remote update download and relaunch path. See docs/ubuntu-desktop-support.md for the matrix and remaining gates.