feat: 다크모드 지원 커스텀 토스트 구현

- showCustomToast() 함수 추가 (AlarmUtils)
- 커스텀 토스트 레이아웃 및 배경 drawable 추가
- values/colors.xml 및 values-night/colors.xml 리소스 사용

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/AlarmUtils.kt

@@ -16,6 +16,26 @@ import java.util.concurrent.TimeUnit
 val SEOUL_ZONE: ZoneId = ZoneId.of("Asia/Seoul")
 const val TAG = "ShiftAlarm"
 
+/**
+ * 다크모드 지원 커스텀 토스트 표시
+ */
+fun showCustomToast(context: Context, message: String, duration: Int = android.widget.Toast.LENGTH_SHORT) {
+ try {
+ val inflater = android.view.LayoutInflater.from(context)
+ val layout = inflater.inflate(R.layout.custom_toast, null)
+ val textView = layout.findViewById<android.widget.TextView>(R.id.toastText)
+ textView.text = message
+
+ val toast = android.widget.Toast(context)
+ toast.duration = duration
+ toast.view = layout
+ toast.setGravity(android.view.Gravity.BOTTOM or android.view.Gravity.CENTER_HORIZONTAL, 0, 100)
+ toast.show()
+ } catch (e: Exception) {
+ // Fallback to default toast if custom toast fails
+ android.widget.Toast.makeText(context, message, duration).show()
+ }
+}
 // ============================================
 // 알람 ID 생성
 // ============================================

app/src/main/res/drawable/bg_custom_toast.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8"?>
+<shape xmlns:android="http://schemas.android.com/apk/res/android"
+    android:shape="rectangle">
+    <solid android:color="@color/surface" />
+    <corners android:radius="12dp" />
+    <stroke
+        android:width="1dp"
+        android:color="@color/outline" />
+</shape>

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

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="wrap_content"
+    android:layout_height="wrap_content"
+    android:orientation="horizontal"
+    android:background="@drawable/bg_custom_toast"
+    android:paddingHorizontal="16dp"
+    android:paddingVertical="10dp"
+    android:gravity="center">
+
+    <TextView
+        android:id="@+id/toastText"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:textSize="14sp"
+        android:textColor="@color/text_primary"
+        android:maxLines="2"
+        android:ellipsize="end" />
+
+</LinearLayout>