feat: add Nerd Font installation, Yazi file manager, and themed Yazi config

- Install JetBrainsMono Nerd Font for icons across all TUI tools
- Add Yazi as terminal file manager with themed config per colorscheme
- Add write_yazi_config() to all 5 theme files
- Theme switcher (archduino-theme) now also updates Yazi
- Add 'y' alias for yazi in shell config
- Update step numbering (9 -> 11 steps) and README

lib/shell-config.sh

@@ -26,6 +26,7 @@ alias acm="arduino-cli monitor"
 alias acb="arduino-cli board list"
 alias lg="lazygit"
 alias v="nvim"
+alias y="yazi"
 alias theme="archduino-theme"
 # ── END ARCHDUINO ───────────────────────────────────────────────'