New Features:
- Recurrences API: Full CRUD + trigger (6 operations)
- Available Budgets API: List and get (2 operations)
- Bills API: Full CRUD + attachments, rules, transactions (8 operations)
- Budgets API: Full CRUD + limits, transactions (15 operations)
- Piggy Banks API: Full CRUD + events, attachments (7 operations)
- Object Groups API: List, get, update, delete + related objects (6 operations)

Improvements:
- Complex nested fixed collections for array handling
- Proper UPDATE operation field optionality
- Date format standardization (YYYY-MM-DD)
- Comprehensive documentation and implementation summaries

Technical:
- 28 files changed, 37,692 insertions
- 6 new API endpoints implemented
- Complete design and implementation documentation