refactor: Modularize build.zsh into separate setup scripts

Separated build.zsh into 3 clear parts:

1. build.zsh (Arch Linux base construction)
   - archiso bootstrap
   - pacstrap base system
   - install base packages
   - install Claude Code

2. cfg/setup-user.sh (User setup)
   - Create ai user
   - Configure sudoers
   - Setup auto-login
   - Configure zshrc and auto-start

3. cfg/setup-claude.sh (Claude/aigpt setup)
   - Install aigpt
   - Configure MCP
   - Setup symlinks
   - Initialize database

Benefits:
- Each file has a single, clear responsibility
- Easier to maintain and modify
- Can skip/customize setup steps if needed
- GitHub Actions simplified to just run build.zsh

cfg/setup-user.sh

@@ -0,0 +1,67 @@
+#!/bin/bash
+# User setup for aios
+# Creates ai user, configures auto-login, sudo, zshrc
+
+ROOTFS="root.x86_64/var/lib/machines/arch"
+
+echo "=== User Setup ==="
+
+# Create default user 'ai'
+echo "Creating user 'ai'..."
+arch-chroot $ROOTFS /bin/sh -c 'useradd -m -G wheel -s /bin/zsh ai'
+arch-chroot $ROOTFS /bin/sh -c 'echo "ai:root" | chpasswd'
+
+# Enable wheel group for sudo (specific commands without password)
+echo "Configuring sudoers..."
+arch-chroot $ROOTFS /bin/sh -c 'echo "%wheel ALL=(ALL:ALL) NOPASSWD: /usr/bin/pacman -Syu --noconfirm, /usr/bin/rm -rf /var/lib/pacman/db.lck, /usr/bin/poweroff, /usr/bin/reboot, /usr/bin/machinectl" >> /etc/sudoers'
+
+# Setup auto-login for user 'ai'
+echo "Setting up auto-login..."
+arch-chroot $ROOTFS /bin/sh -c 'mkdir -p /etc/systemd/system/getty@tty1.service.d'
+cat > $ROOTFS/etc/systemd/system/getty@tty1.service.d/override.conf <<'EOF'
+[Service]
+ExecStart=
+ExecStart=-/usr/bin/agetty --autologin ai --noclear %I $TERM
+EOF
+
+# Copy .zshrc for root
+echo "Copying zshrc..."
+cp -rf ./cfg/zshrc $ROOTFS/root/.zshrc
+
+# Copy .zshrc for user 'ai'
+cp -rf ./cfg/zshrc $ROOTFS/home/ai/.zshrc
+
+# Add claude auto-start for ai user (login shell only)
+cat >> $ROOTFS/home/ai/.zshrc <<'EOF'
+
+# Auto-start claude in interactive login shell
+if [[ -o login ]] && [[ -o interactive ]]; then
+    if command -v claude &>/dev/null; then
+        exec claude
+    fi
+fi
+EOF
+
+arch-chroot $ROOTFS /bin/sh -c 'chown ai:ai /home/ai/.zshrc'
+
+# Copy aios startup script
+cp -rf ./cfg/aios.zsh $ROOTFS/usr/local/bin/aios-startup
+arch-chroot $ROOTFS /bin/sh -c 'chmod +x /usr/local/bin/aios-startup'
+
+# Create default config directory and file for user 'ai'
+arch-chroot $ROOTFS /bin/sh -c 'mkdir -p /home/ai/.config/syui/ai/os'
+cat > $ROOTFS/home/ai/.config/syui/ai/os/config.json <<'EOF'
+{
+  "shell": false
+}
+EOF
+arch-chroot $ROOTFS /bin/sh -c 'chown -R ai:ai /home/ai/.config'
+
+# Update .zshrc to source startup script
+cat >> $ROOTFS/home/ai/.zshrc <<'EOF'
+
+# aios startup
+source /usr/local/bin/aios-startup
+EOF
+
+echo "✓ User setup complete"