refactor: restructure installation to modular architecture

- Remove monolithic bootstrap.sh in favor of modular design
- Add install.sh as new main entry point with improved UX
- Split functionality into focused modules:
  - lib/common.sh: shared utilities and environment detection
  - lib/packages.sh: base system packages
  - lib/neovim.sh: Neovim and LazyVim setup
  - lib/arduino.sh: Arduino CLI and board cores
  - lib/git.sh: Git and Lazygit configuration
  - lib/shell-config.sh: Zsh and shell environment
  - lib/starship.sh: Starship prompt setup
  - lib/zellij.sh: Zellij terminal multiplexer
  - lib/scaffold.sh: project scaffolding utilities
- Update README with new installation instructions and architecture
- Improve error handling and user feedback across modules
- Maintain compatibility with both Arch Linux and Ubuntu/WSL2

This modular approach enables better maintainability, testing,
and allows users to selectively run components as needed.

lib/shell-config.sh

@@ -0,0 +1,50 @@
+#!/bin/bash
+# Shell config (.zshrc) and WSL2 extras
+
+step "Finalizing shell config"
+
+# Append archduino block to .zshrc if not already present
+if ! grep -q "ARCHDUINO" ~/.zshrc 2>/dev/null; then
+  cat >>~/.zshrc <<'ZSHRC'
+
+# ── ARCHDUINO CONFIG ────────────────────────────────────────────
+plugins=(git zsh-autosuggestions zsh-syntax-highlighting)
+
+export PATH="$HOME/.local/bin:$PATH"
+export EDITOR="nvim"
+export VISUAL="nvim"
+
+eval "$(starship init zsh)"
+
+# Auto-start Zellij
+if [[ -z "$ZELLIJ" ]]; then
+  zellij attach --create archduino
+fi
+
+# Arduino aliases
+alias adev="zellij --layout arduino"
+alias ac="arduino-cli"
+alias acc="arduino-cli compile"
+alias acu="arduino-cli upload"
+alias acm="arduino-cli monitor"
+alias acb="arduino-cli board list"
+alias lg="lazygit"
+alias v="nvim"
+# ── END ARCHDUINO ───────────────────────────────────────────────
+ZSHRC
+  info "Shell config updated"
+else
+  info "Shell config already contains Archduino block"
+fi
+
+# ── WSL2 extras ─────────────────────────────────────────────────
+if $IS_WSL; then
+  step "WSL2 extras"
+  warn "USB passthrough requires usbipd-win on Windows."
+  warn "Install it with:  winget install usbipd"
+  warn "Then attach your Arduino:  usbipd attach --wsl --busid <BUSID>"
+
+  # Add user to dialout for serial access
+  sudo usermod -aG dialout "$USER" 2>/dev/null || true
+  sudo usermod -aG uucp "$USER" 2>/dev/null || true
+fi