Refactor habit entries: remove soft delete and add smart pagination

Remove soft delete from HabitEntry:
- Eliminate DeletedAt field from entity and database
- Change UnmarkHabit from soft delete to hard delete
- Simplify all queries removing deleted_at checks
- Update migration to remove deleted_at column

Add date filtering and smart pagination to GetHabitEntries:
- Support optional from/to date parameters
- Implement intelligent pagination rules:
  * No date range: pagination required
  * Date range > 1 year: pagination required
  * Date range ≤ 1 year: pagination optional
- Pagination defaults (page=1, limit=50) only when required
- Return metadata with total count, page, and limit

Technical improvements:
- Cleaner codebase without soft delete complexity
- Better performance (no filtering in queries)
- More intuitive API with flexible pagination
- Comprehensive test coverage for validation rules

internal/domain/entities/habit_entry.go

@@ -8,7 +8,6 @@ type HabitEntry struct {
 	ScheduledDate time.Time
 	CompletedAt   time.Time
 	Value         *float64
-	DeletedAt     *time.Time
 }
 
 func NewHabitEntry(habitID string, scheduledDate time.Time, value *float64) *HabitEntry {
@@ -19,12 +18,3 @@ func NewHabitEntry(habitID string, scheduledDate time.Time, value *float64) *Hab
 		Value:         value,
 	}
 }
-
-func (e *HabitEntry) Delete() {
-	now := time.Now()
-	e.DeletedAt = &now
-}
-
-func (e *HabitEntry) IsDeleted() bool {
-	return e.DeletedAt != nil
-}