v0.2.3: Replace Mutter with XFWM4, polish desktop and CLI experience

- Swap Mutter for XFWM4 to get proper window title bars with
  close/minimize/maximize/drag/resize support
- Install noVNC v1.6.0 from GitHub (apt package has version mismatches
  on Ubuntu 24.04) with custom compeek-vnc.html viewer
- Add dark-themed desktop: gradient wallpaper, tint2 panel with app
  launchers (Firefox, Terminal, Thunar), GTK dark theme
- Always open Firefox in full/browser modes and maximize on startup
- Add branded homepage (dark gradient with compeek branding) as Firefox
  default
- Add fullscreen toggle and "New Tab" button to desktop viewer toolbar
- Redesign CLI output with ANSI colors, spinner animation, structured
  layout, and beautiful help text
- Fix selector button padding in WorkflowPanel