⚡️(admin) improve recording access select component performance

Replace the basic select component that loaded thousands of options into the
DOM with a smarter component supporting dynamic loading and search.

With large user bases, linking users to recording access caused massive option
lists to render, severely impacting performance. This change dramatically
improves page loading speed.

src/backend/core/admin.py

@@ -142,6 +142,7 @@ class RecordingAccessInline(admin.TabularInline):
 
     model = models.RecordingAccess
     extra = 0
+    autocomplete_fields = ["user"]
 
 
 @admin.action(description=_("Resend notification to external service"))