Complete CRUD operations for habits

Implement all missing endpoints for full habit management:
- GET /api/v1/habits - List all user habits
- GET /api/v1/habits/{id} - Get specific habit
- PUT /api/v1/habits/{id} - Update habit
- DELETE /api/v1/habits/{id} - Archive habit (soft delete)
- GET /api/v1/habits/{id}/entries - Get habit entry history
- DELETE /api/v1/habits/{id}/entries/{date} - Unmark habit (soft delete entry)

All endpoints include:
- TDD approach with comprehensive test coverage
- JWT authentication and ownership validation
- Proper error handling (404, 403, 400, 500)
- Clean architecture with separated commands/queries

internal/application/queries/get_habit_by_id.go

@@ -0,0 +1,44 @@
+package queries
+
+import (
+	"context"
+
+	"apocapoc-api/internal/domain/repositories"
+	"apocapoc-api/internal/shared/errors"
+)
+
+type GetHabitByIDQuery struct {
+	HabitID string
+	UserID  string
+}
+
+type GetHabitByIDHandler struct {
+	habitRepo repositories.HabitRepository
+}
+
+func NewGetHabitByIDHandler(habitRepo repositories.HabitRepository) *GetHabitByIDHandler {
+	return &GetHabitByIDHandler{
+		habitRepo: habitRepo,
+	}
+}
+
+func (h *GetHabitByIDHandler) Handle(ctx context.Context, query GetHabitByIDQuery) (*HabitDTO, error) {
+	habit, err := h.habitRepo.FindByID(ctx, query.HabitID)
+	if err != nil {
+		return nil, err
+	}
+
+	if habit.UserID != query.UserID {
+		return nil, errors.ErrUnauthorized
+	}
+
+	return &HabitDTO{
+		ID:           habit.ID,
+		Name:         habit.Name,
+		Type:         string(habit.Type),
+		Frequency:    string(habit.Frequency),
+		TargetValue:  habit.TargetValue,
+		CarryOver:    habit.CarryOver,
+		SpecificDays: habit.SpecificDays,
+	}, nil
+}