Added item flag name import/export support - fixes #3

[philayres]

Summary

Adds import support for item flag names in app type configurations and test coverage for import round-trip. Supersedes #1037.

Changes

Import implementation:

• Added import_config_sub_items 'associated_item_flag_names', %w[name item_type] to import_set in app/models/admin/app_type_import.rb
• Placed after associated_general_selections import (item flags depend on table types being available)

Import test coverage:

• Added test verifying item flag names are created during import
• Exports a config with item flags, injects a new flag name, imports to a new app type, and verifies the flag was created

Spec comment:

• Added descriptive comment block to import spec file

Files changed

• app/models/admin/app_type_import.rb — Added import line for associated_item_flag_names
• spec/models/admin/app_type_import_spec.rb — Added import round-trip test and comment