fix: 연차 저장 및 계산 로직 수정

- calculateUsedAnnualLeave()에서 Seoul 타임존 명시
- FragmentSettingsLab 토스트를 커스텀 토스트로 변경
- 연차 저장 시 남은 연차 자동 계산 로직 개선

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

app/src/main/java/com/example/shiftalarm/FragmentSettingsLab.kt

@@ -55,23 +55,23 @@ class FragmentSettingsLab : Fragment() {
         }
     }
 
-    private fun setupSaveButton() {
-        binding.btnSaveAnnualLeave.setOnClickListener {
-            val totalDays = binding.npTotalDays.value.toFloat()
-            
-            lifecycleScope.launch {
-                val repo = ShiftRepository(requireContext())
-                
-                repo.recalculateAndSaveAnnualLeave(totalDays)
-                
-                val updated = repo.getAnnualLeave()
-                updated?.let {
-                    binding.tvRemainingDays.text = String.format("%.1f", it.remainingDays)
-                    Toast.makeText(requireContext(), "연차가 저장되었습니다. (남은 연차: ${String.format("%.1f", it.remainingDays)}일)", Toast.LENGTH_SHORT).show()
-                }
-            }
-        }
-    }
+ private fun setupSaveButton() {
+ binding.btnSaveAnnualLeave.setOnClickListener {
+ val totalDays = binding.npTotalDays.value.toFloat()
+
+ lifecycleScope.launch {
+ val repo = ShiftRepository(requireContext())
+
+ repo.recalculateAndSaveAnnualLeave(totalDays)
+
+ val updated = repo.getAnnualLeave()
+ updated?.let {
+ binding.tvRemainingDays.text = String.format("%.1f", it.remainingDays)
+ showCustomToast(requireContext(), "연차가 저장되었습니다. (남은 연차: ${String.format("%.1f", it.remainingDays)}일)")
+ }
+ }
+ }
+ }
 
     override fun onDestroyView() {
         super.onDestroyView()