feat: Implement secure database operations and caching for encrypted accounts

app/src/main/java/com/rosetta/messenger/database/RosettaDatabase.kt

@@ -0,0 +1,34 @@
+package com.rosetta.messenger.database
+
+import android.content.Context
+import androidx.room.Database
+import androidx.room.Room
+import androidx.room.RoomDatabase
+
+@Database(
+    entities = [EncryptedAccountEntity::class],
+    version = 1,
+    exportSchema = false
+)
+abstract class RosettaDatabase : RoomDatabase() {
+    abstract fun accountDao(): AccountDao
+
+    companion object {
+        @Volatile
+        private var INSTANCE: RosettaDatabase? = null
+
+        fun getDatabase(context: Context): RosettaDatabase {
+            return INSTANCE ?: synchronized(this) {
+                val instance = Room.databaseBuilder(
+                    context.applicationContext,
+                    RosettaDatabase::class.java,
+                    "rosetta_secure.db"
+                )
+                    .setJournalMode(JournalMode.WRITE_AHEAD_LOGGING) // WAL mode for performance
+                    .build()
+                INSTANCE = instance
+                instance
+            }
+        }
+    }
+}