ca2533d4df
Replace generic string types with strongly-typed value objects throughout the application layer. This change ensures compile-time type checking and automatic validation during JSON deserialization. Changes: - Add JSON marshaling/unmarshaling to HabitType and Frequency value objects - Update all DTOs to use typed fields instead of strings - Update commands and queries to use proper types - Remove unnecessary string conversions - Add comprehensive JSON serialization tests - Fix existing tests to work with typed fields Benefits: - Type safety: compiler catches invalid usage - Automatic validation: invalid values rejected during JSON parsing - Better code documentation and self-explanatory APIs - Reduced runtime errors