Implement SQLite persistence layer (TDD)

- Add SQLite and UUID dependencies (go-sqlite3, google/uuid)
- Create database connection with automatic migrations
- Implement UserRepository with full CRUD operations
- Implement HabitRepository with JSON serialization for arrays
- Implement HabitEntryRepository with date range queries
- Add comprehensive test coverage for all repositories
- Fix User entity to default timezone to UTC when empty
- All tests passing with TDD approach (Red-Green-Refactor)

internal/domain/entities/habit_entry_test.go

@@ -55,7 +55,7 @@ func TestHabitEntry_SoftDelete(t *testing.T) {
 		t.Error("New entry should not be deleted")
 	}
 
-	entry.SoftDelete()
+	entry.Delete()
 
 	if entry.DeletedAt == nil {
 		t.Error("Entry should be deleted after calling SoftDelete()")