Add rustfmt.toml with tab_spaces = 2 and reformat all source files, tests, and README code examples to use 2-space indentation.
Implement App model and three endpoint methods: list_apps (paginated), get_app (by ID), and batch_get_apps (up to 100 by IDs). Add comprehensive tests for success, pagination, not-found, and batch scenarios.
Stevan Freeborn