feat: 연차 관리 기능 추가 (AnnualLeave 엔티티, DAO, Repository)

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/ShiftRepository.kt

@@ -57,4 +57,47 @@ class ShiftRepository(private val context: Context) {
     suspend fun clearAllCustomAlarms() = withContext(Dispatchers.IO) {
         dao.clearCustomAlarms()
     }
+
+    // Annual Leave
+    suspend fun calculateUsedAnnualLeave(): Float = withContext(Dispatchers.IO) {
+        val currentYear = java.time.Year.now().toString()
+        val overrides = dao.getAllOverrides()
+        
+        var usedDays = 0f
+        
+        for (override in overrides) {
+            if (override.date.startsWith(currentYear)) {
+                when (override.shift) {
+                    "연차" -> usedDays += 1f
+                    "반년" -> usedDays += 0.5f
+                }
+            }
+        }
+        
+        usedDays
+    }
+
+    suspend fun getAnnualLeave(): AnnualLeave? = withContext(Dispatchers.IO) {
+        dao.getAnnualLeave()
+    }
+
+    suspend fun recalculateAndSaveAnnualLeave(totalDays: Float) {
+        val usedDays = calculateUsedAnnualLeave()
+        val remainingDays = totalDays - usedDays
+        
+        dao.insertAnnualLeave(AnnualLeave(
+            id = 1,
+            totalDays = totalDays,
+            remainingDays = remainingDays
+        ))
+    }
+
+    suspend fun updateRemainingAnnualLeave() {
+        val annualLeave = dao.getAnnualLeave()
+        annualLeave?.let {
+            val usedDays = calculateUsedAnnualLeave()
+            val remainingDays = it.totalDays - usedDays
+            dao.insertAnnualLeave(it.copy(remainingDays = remainingDays))
+        }
+    }
 }