refactor: Rename Property/PropertyType to CustomFieldValue/CustomField

Complete refactoring of resources, database tables, code references, tests, and documentation for improved naming consistency.

priv/repo/seeds.exs

@@ -36,7 +36,7 @@ for attrs <- [
         required: true
       }
     ] do
-  Membership.create_property_type!(
+  Membership.create_custom_field!(
     attrs,
     upsert?: true,
     upsert_identity: :unique_name
@@ -182,7 +182,7 @@ end)
 
 IO.puts("✅ Seeds completed successfully!")
 IO.puts("📝 Created sample data:")
-IO.puts("   - Property types: String, Date, Boolean, Email")
+IO.puts("   - Custom fields: String, Date, Boolean, Email")
 IO.puts("   - Admin user: admin@mv.local (password: testpassword)")
 IO.puts("   - Sample members: Hans, Greta, Friedrich")