Add robust input validation system and fix test suite

- Add comprehensive validation package with email (RFC 5322), password strength, and IANA timezone validation
- Implement strict password requirements: min 8 chars, uppercase, lowercase, digit, special character
- Integrate validation into RegisterUserHandler with complete test coverage (59 validation tests + 25 handler tests)
- Fix pre-existing test failures:
  - Remove tests for non-existent HabitEntry.DeletedAt and Delete() methods
  - Replace deprecated HabitTypeQuantity with HabitTypeValue
  - Add missing FindByHabitIDAndDateRange mock implementation
- Remove hardcoded localhost:8080 from Swagger config for self-hosted flexibility

internal/application/queries/get_habit_entries_test.go

@@ -20,6 +20,10 @@ func (m *mockEntryRepoWithFindByHabitID) FindByHabitID(ctx context.Context, habi
 	return m.entries, nil
 }
 
+func (m *mockEntryRepoWithFindByHabitID) FindByHabitIDAndDateRange(ctx context.Context, habitID string, from, to time.Time) ([]*entities.HabitEntry, error) {
+	return m.entries, nil
+}
+
 func TestGetHabitEntriesHandler_ReturnsEntriesSuccessfully(t *testing.T) {
 	habit := entities.NewHabit("user-123", "Exercise", value_objects.HabitTypeBoolean, value_objects.FrequencyDaily, false)
 	habit.ID = "habit-1"