Move default install location to /opt/stegasoo

- setup.sh: Install to /opt/stegasoo with proper permissions
- first-boot-wizard.sh: Use /opt/stegasoo
- stegasoo-wizard.sh: Check /opt first, fallback to home dirs
- sanitize-for-image.sh: Handle both /opt and home locations

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

rpi/first-boot-wizard.sh

@@ -18,7 +18,7 @@ BOLD='\033[1m'
 NC='\033[0m'
 
 # Configuration
-INSTALL_DIR="$HOME/stegasoo"
+INSTALL_DIR="/opt/stegasoo"
 FLAG_FILE="/etc/stegasoo-first-boot"
 PROFILE_HOOK="/etc/profile.d/stegasoo-wizard.sh"