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/commands/unmark_habit.go

@@ -0,0 +1,78 @@
+package commands
+
+import (
+	"context"
+	"time"
+
+	"apocapoc-api/internal/domain/entities"
+	"apocapoc-api/internal/domain/repositories"
+	"apocapoc-api/internal/shared/errors"
+)
+
+type UnmarkHabitCommand struct {
+	HabitID       string
+	UserID        string
+	ScheduledDate time.Time
+}
+
+type UnmarkHabitHandler struct {
+	habitRepo repositories.HabitRepository
+	entryRepo repositories.HabitEntryRepository
+}
+
+func NewUnmarkHabitHandler(
+	habitRepo repositories.HabitRepository,
+	entryRepo repositories.HabitEntryRepository,
+) *UnmarkHabitHandler {
+	return &UnmarkHabitHandler{
+		habitRepo: habitRepo,
+		entryRepo: entryRepo,
+	}
+}
+
+func (h *UnmarkHabitHandler) Handle(ctx context.Context, cmd UnmarkHabitCommand) error {
+	// Verify habit exists and user owns it
+	habit, err := h.habitRepo.FindByID(ctx, cmd.HabitID)
+	if err != nil {
+		return err
+	}
+
+	if habit.UserID != cmd.UserID {
+		return errors.ErrUnauthorized
+	}
+
+	// Find the entry for the scheduled date
+	// We search within the same day
+	startOfDay := time.Date(
+		cmd.ScheduledDate.Year(),
+		cmd.ScheduledDate.Month(),
+		cmd.ScheduledDate.Day(),
+		0, 0, 0, 0,
+		cmd.ScheduledDate.Location(),
+	)
+	endOfDay := startOfDay.Add(24 * time.Hour)
+
+	entries, err := h.entryRepo.FindByHabitIDAndDateRange(ctx, cmd.HabitID, startOfDay, endOfDay)
+	if err != nil {
+		return err
+	}
+
+	// Find the active entry for this date
+	var targetEntry *entities.HabitEntry
+	for _, entry := range entries {
+		if entry.ScheduledDate.Equal(cmd.ScheduledDate) && entry.DeletedAt == nil {
+			targetEntry = entry
+			break
+		}
+	}
+
+	if targetEntry == nil {
+		return errors.ErrNotFound
+	}
+
+	// Soft delete the entry
+	now := time.Now()
+	targetEntry.DeletedAt = &now
+
+	return h.entryRepo.Update(ctx, targetEntry)
+}