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/arduino.sh

@@ -0,0 +1,36 @@
+#!/bin/bash
+# Step 7: Arduino CLI + board cores
+
+step "7/9 — Installing Arduino CLI + board cores"
+
+if ! command -v arduino-cli &>/dev/null; then
+  if $IS_ARCH; then
+    $PKG_INSTALL arduino-cli
+  else
+    curl -kfsSL https://raw.githubusercontent.com/arduino/arduino-cli/master/install.sh | BINDIR=/usr/local/bin sudo sh
+  fi
+fi
+info "Arduino CLI installed: $(arduino-cli version 2>/dev/null | head -1)"
+
+arduino-cli config init 2>/dev/null || true
+
+# Add ESP board manager URLs
+arduino-cli config add board_manager.additional_urls \
+  https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json 2>/dev/null || true
+arduino-cli config add board_manager.additional_urls \
+  https://arduino.esp8266.com/stable/package_esp8266com_index.json 2>/dev/null || true
+
+arduino-cli core update-index
+
+info "Installing AVR core..."
+arduino-cli core install arduino:avr
+
+info "Installing ESP32 core..."
+arduino-cli core install esp32:esp32
+
+info "Installing ESP8266 core..."
+arduino-cli core install esp8266:esp8266
+
+# Common libs
+arduino-cli lib install "Servo" "ArduinoJson" "Adafruit Unified Sensor" "DHT sensor library" 2>/dev/null || true
+info "Board cores & libraries installed"