feat: 토요일 연장근무 계산 기능 추가

- ShiftRepository에 getSaturdayOvertimeHours() 메소드 추가
- FragmentSettingsLab에 토요일 연장근무 시간 표시 카드 추가
- 토요일 수 * 2시간 계산 로직 구현

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

@@ -31,6 +31,7 @@ class FragmentSettingsLab : Fragment() {
         
         setupSpinner()
         loadAnnualLeave()
+        loadSaturdayOvertime()
     }
 
     private fun setupSpinner() {
@@ -106,6 +107,14 @@ class FragmentSettingsLab : Fragment() {
         }
     }
 
+    private fun loadSaturdayOvertime() {
+        lifecycleScope.launch {
+            val repo = ShiftRepository(requireContext())
+            val overtimeHours = repo.getSaturdayOvertimeHours()
+            binding.tvSaturdayOvertime.text = "$overtimeHours"
+        }
+    }
+
     override fun onDestroyView() {
         super.onDestroyView()
         _binding = null

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

@@ -108,4 +108,19 @@ class ShiftRepository(private val context: Context) {
             ))
         }
     }
+
+    suspend fun getSaturdayOvertimeHours(): Int = withContext(Dispatchers.IO) {
+        val currentYear = LocalDate.now().year
+        val allOverrides = dao.getAllOverrides()
+        
+        val saturdayWorkDays = allOverrides.filter { override ->
+            val date = LocalDate.parse(override.date)
+            date.year == currentYear &&
+            date.dayOfWeek == java.time.DayOfWeek.SATURDAY &&
+            override.shift != "휴무" &&
+            override.shift != "휴가"
+        }
+        
+        saturdayWorkDays.size * 2
+    }
 }

app/src/main/res/layout/fragment_settings_lab.xml

@@ -123,14 +123,64 @@
         android:layout_marginBottom="8dp"
         android:gravity="center"/>
 
-    <!-- 기능추가중 Notice -->
+    <!-- Saturday Overtime Display -->
+    <androidx.cardview.widget.CardView
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:layout_marginBottom="16dp"
+        app:cardCornerRadius="12dp"
+        app:cardElevation="2dp"
+        app:cardBackgroundColor="@color/surface">
+
+        <LinearLayout
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:orientation="horizontal"
+            android:padding="16dp"
+            android:gravity="center_vertical">
+
+            <TextView
+                android:layout_width="0dp"
+                android:layout_height="wrap_content"
+                android:layout_weight="1"
+                android:text="토요일 연장근무"
+                android:textSize="14sp"
+                android:textColor="@color/text_secondary"/>
+
+            <LinearLayout
+                android:layout_width="wrap_content"
+                android:layout_height="wrap_content"
+                android:orientation="horizontal"
+                android:gravity="bottom">
+
+                <TextView
+                    android:id="@+id/tvSaturdayOvertime"
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="0"
+                    android:textSize="28sp"
+                    android:textStyle="bold"
+                    android:textColor="@color/shift_red"/>
+
+                <TextView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="시간"
+                    android:textSize="14sp"
+                    android:textColor="@color/text_tertiary"
+                    android:layout_marginStart="4dp"/>
+            </LinearLayout>
+        </LinearLayout>
+    </androidx.cardview.widget.CardView>
+
+    <!-- Calculation Info -->
     <TextView
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
-        android:text="기능추가중"
-        android:textSize="11sp"
-        android:textColor="@color/primary"
-        android:layout_marginBottom="24dp"
+        android:text="※ 토요일 근무: 1일당 2시간 연장근무 계산"
+        android:textSize="12sp"
+        android:textColor="@color/text_tertiary"
+        android:layout_marginBottom="8dp"
         android:gravity="center"/>
 
 </LinearLayout>