Enhanced install.sh to properly handle updates and migrations:
**Update Detection & Service Management:**
- Detect old Node.js-based installations (v3.x) via package.json/node_modules
- Stop running service before updating binary
- Restart service after successful update if it was running
- Preserve /etc/nupst/config.json during updates
**Migration from v3.x to v4.0:**
- Clean up old Node.js installation files:
- node_modules/, vendor/, dist_ts/ directories
- package.json, package-lock.json, pnpm-lock.yaml
- tsconfig.json, setup.sh, bin/ directory
- Inform user about migration with helpful feedback
- Link to migration guide documentation
**User Experience Improvements:**
- Show different messages for new installs vs updates
- Inform about v3.x → v4.0 migration when detected
- Display migration guide link for old installations
- Show service restart status
- Provide context-aware next steps based on config presence
**Safety Features:**
- Ask for confirmation before replacing existing installation (interactive mode)
- Preserve user configuration in /etc/nupst/
- Handle service state properly (stop → update → restart)
- Graceful cleanup with error suppression (|| true)
This ensures seamless updates from any version (including v3.x Node.js installs)
to v4.0+ Deno-based binaries without manual intervention or data loss.