fix: DB 마이그레이션 추가 및 연차 저장/다크모드/달력 UI 개선

- DB 마이그레이션으로 기존 알람 데이터 보존
- 연차 저장 문제 수정 (원래대로/연차 설정 시 updateRemainingAnnualLeave 호출)
- 달력 5행 스크롤 없이 표시 (85dp 높이)
- 알람 편집/월년 선택 다크모드 지원
- 설정 앱정보 버전 동기화 표시

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/AppDatabase.kt

@@ -1,7 +1,11 @@
 package com.example.shiftalarm
 
 import android.content.Context
-import androidx.room.*
+import androidx.room.Database
+import androidx.room.Room
+import androidx.room.RoomDatabase
+import androidx.room.migration.Migration
+import androidx.sqlite.db.SupportSQLiteDatabase
 
 @Database(entities = [ShiftOverride::class, DailyMemo::class, CustomAlarm::class, AnnualLeave::class], version = 4, exportSchema = false)
 abstract class AppDatabase : RoomDatabase() {
@@ -11,6 +15,23 @@ abstract class AppDatabase : RoomDatabase() {
         @Volatile
         private var INSTANCE: AppDatabase? = null
 
+        // Migration from version 3 to 4: Add AnnualLeave table
+        private val MIGRATION_3_4 = object : Migration(3, 4) {
+            override fun migrate(database: SupportSQLiteDatabase) {
+                // Create AnnualLeave table
+                database.execSQL(
+                    """
+                    CREATE TABLE IF NOT EXISTS annual_leave (
+                        id INTEGER PRIMARY KEY NOT NULL,
+                        totalDays REAL NOT NULL,
+                        remainingDays REAL NOT NULL,
+                        updatedAt INTEGER NOT NULL
+                    )
+                    """.trimIndent()
+                )
+            }
+        }
+
         fun getDatabase(context: Context): AppDatabase {
             return INSTANCE ?: synchronized(this) {
                 val instance = Room.databaseBuilder(
@@ -18,7 +39,7 @@ abstract class AppDatabase : RoomDatabase() {
                     AppDatabase::class.java,
                     "shift_database"
                 )
-                .fallbackToDestructiveMigration() // Simple for now
+                .addMigrations(MIGRATION_3_4)
                 .build()
                 INSTANCE = instance
                 instance