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/fonts.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+# Step 2: Nerd Font installation
+
+step "2/11 — Installing Nerd Font"
+
+FONT_DIR="$HOME/.local/share/fonts/NerdFonts"
+FONT_NAME="JetBrainsMono"
+
+if fc-list 2>/dev/null | grep -qi "JetBrainsMono Nerd"; then
+  info "JetBrainsMono Nerd Font already installed"
+else
+  mkdir -p "$FONT_DIR"
+  curl -ksSLo /tmp/JetBrainsMono.tar.xz \
+    "https://github.com/ryanoasis/nerd-fonts/releases/latest/download/JetBrainsMono.tar.xz"
+  tar xf /tmp/JetBrainsMono.tar.xz -C "$FONT_DIR"
+  rm -f /tmp/JetBrainsMono.tar.xz
+  fc-cache -f 2>/dev/null || true
+  info "JetBrainsMono Nerd Font installed to $FONT_DIR"
+fi
+
+if $IS_WSL; then
+  warn "WSL detected: You must also install a Nerd Font on the Windows side."
+  warn "Download from: https://www.nerdfonts.com/font-downloads"
+  warn "Then set 'JetBrainsMono Nerd Font' in your terminal settings (Windows Terminal, etc.)."
+fi