test: add comprehensive sheet management test suite

- Add test_sheet_creation_management_and_persistence with 3 test functions:
  - Main test covering sheet creation, input/mapping management, persistence, and deletion
  - Error condition testing for invalid operations
  - Serialization testing through vault operations
- Test coverage includes:
  - Sheet creation with member validation
  - Input package addition and removal
  - Mapping entry management
  - File persistence and reloading
  - Safe deletion to trash and restoration
  - Permanent deletion
  - Error handling for invalid operations
- Follows existing test patterns and uses proper getter methods for private fields

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