v1.2: Meta mode overlay, `tmux-menus` plugin

Please install firmware version 3.4 for this Buildroot release.

Buildroot README now contains setup and usage instructions.

• Added Python 3 pip packages.
• New key shortcuts:
  • Short hold (1 second) of Berry key opens Meta mode overlay
  • Short hold (1 second) of End Call key opens tmux-menus plugin
  • See beepy-kbd documentation for full keybindings.
• Fixes Symbol entry for Unicode characters in the terminal.
• Increases default grayscale cutoff for better nmtui rendering.