feat: initialize GaCy Android project foundation (Kotlin, Jetpack Compose, Material 3)

app/src/main/java/com/gacy/android/GaCyApplication.kt

@@ -0,0 +1,37 @@
+package com.gacy.android
+
+import android.app.Application
+import android.app.NotificationChannel
+import android.app.NotificationManager
+import android.os.Build
+
+class GaCyApplication : Application() {
+
+    companion object {
+        const val CHANNEL_ID = "gacy_server_channel"
+        const val CHANNEL_NAME = "GaCy Server Service"
+        lateinit var instance: GaCyApplication
+            private set
+    }
+
+    override fun onCreate() {
+        super.onCreate()
+        instance = this
+        createNotificationChannel()
+    }
+
+    private fun createNotificationChannel() {
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+            val channel = NotificationChannel(
+                CHANNEL_ID,
+                CHANNEL_NAME,
+                NotificationManager.IMPORTANCE_LOW
+            ).apply {
+                description = "Background service for GaCy Game Server & Proxy"
+                setShowBadge(false)
+            }
+            val manager = getSystemService(NotificationManager::class.java)
+            manager?.createNotificationChannel(channel)
+        }
+    }
+}