refactor: Modernize portal JS from jQuery/AMD to vanilla JS IIFE

- portal_interactive_features.js: Converted from odoo.define/jQuery to vanilla JS IIFE
  * PortalInventory widget for AJAX filtering/pagination/search
  * PortalDocumentRetrieval wizard for multi-step forms
  * PortalBarcodeScanner for barcode input
  * All use native DOM APIs, no jQuery dependencies

- portal_search.js: Converted from odoo.define/jQuery to vanilla JS IIFE
  * Autocomplete search with debouncing
  * Native XHR for Odoo RPC calls
  * HTML escaping for security

- Legacy files preserved as *_LEGACY.js for reference

Benefits:
- No jQuery dependency (Odoo 18+ compatible)
- Smaller bundle size
- Better performance with native APIs
- Modern IIFE pattern for portal scripts

Author: John75SunCity