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_test.go

@@ -0,0 +1,104 @@
+package queries
+
+import (
+	"context"
+	"testing"
+
+	"apocapoc-api/internal/domain/entities"
+	"apocapoc-api/internal/domain/value_objects"
+	"apocapoc-api/internal/shared/errors"
+)
+
+type mockHabitRepoWithFindByID struct {
+	mockHabitRepo
+	habitToReturn *entities.Habit
+	errorToReturn error
+}
+
+func (m *mockHabitRepoWithFindByID) FindByID(ctx context.Context, id string) (*entities.Habit, error) {
+	if m.errorToReturn != nil {
+		return nil, m.errorToReturn
+	}
+	return m.habitToReturn, nil
+}
+
+func TestGetHabitByIDHandler_ReturnsHabitSuccessfully(t *testing.T) {
+	targetValue := 5.0
+	habit := entities.NewHabit("user-123", "Drink Water", value_objects.HabitTypeQuantity, value_objects.FrequencyDaily, true)
+	habit.ID = "habit-1"
+	habit.TargetValue = &targetValue
+
+	habitRepo := &mockHabitRepoWithFindByID{
+		habitToReturn: habit,
+	}
+
+	handler := NewGetHabitByIDHandler(habitRepo)
+
+	query := GetHabitByIDQuery{
+		HabitID: "habit-1",
+		UserID:  "user-123",
+	}
+
+	result, err := handler.Handle(context.Background(), query)
+
+	if err != nil {
+		t.Fatalf("Expected no error, got %v", err)
+	}
+
+	if result.ID != "habit-1" {
+		t.Errorf("Expected ID habit-1, got %s", result.ID)
+	}
+
+	if result.Name != "Drink Water" {
+		t.Errorf("Expected name 'Drink Water', got %s", result.Name)
+	}
+
+	if result.Type != string(value_objects.HabitTypeQuantity) {
+		t.Errorf("Expected type %s, got %s", value_objects.HabitTypeQuantity, result.Type)
+	}
+
+	if result.TargetValue == nil || *result.TargetValue != 5.0 {
+		t.Errorf("Expected target value 5.0, got %v", result.TargetValue)
+	}
+}
+
+func TestGetHabitByIDHandler_ReturnsErrorWhenHabitNotFound(t *testing.T) {
+	habitRepo := &mockHabitRepoWithFindByID{
+		errorToReturn: errors.ErrNotFound,
+	}
+
+	handler := NewGetHabitByIDHandler(habitRepo)
+
+	query := GetHabitByIDQuery{
+		HabitID: "non-existent",
+		UserID:  "user-123",
+	}
+
+	_, err := handler.Handle(context.Background(), query)
+
+	if err != errors.ErrNotFound {
+		t.Errorf("Expected ErrNotFound, got %v", err)
+	}
+}
+
+func TestGetHabitByIDHandler_ReturnsErrorWhenUserDoesNotOwnHabit(t *testing.T) {
+	habit := entities.NewHabit("user-123", "Exercise", value_objects.HabitTypeBoolean, value_objects.FrequencyDaily, false)
+	habit.ID = "habit-1"
+
+	habitRepo := &mockHabitRepoWithFindByID{
+		habitToReturn: habit,
+	}
+
+	handler := NewGetHabitByIDHandler(habitRepo)
+
+	query := GetHabitByIDQuery{
+		HabitID: "habit-1",
+		UserID:  "user-456", // Different user
+	}
+
+	_, err := handler.Handle(context.Background(), query)
+
+	if err != errors.ErrUnauthorized {
+		t.Errorf("Expected ErrUnauthorized, got %v", err)
+	}
+}