Fix polling interval settings and add release build signing

- Fix polling interval not reflecting saved value (use SharingStarted.Eagerly)
- Add release build signing configuration with keystore
- Add key.properties to .gitignore for security
- Add ProGuard rules for JSpecify annotations

app/src/main/java/com/hotdeal/alarm/presentation/main/MainViewModel.kt

@@ -26,9 +26,9 @@ class MainViewModel @Inject constructor(
     private val _uiState = MutableStateFlow<MainUiState>(MainUiState.Loading)
     val uiState: StateFlow<MainUiState> = _uiState.asStateFlow()
     
-    // 폴� 주기
+    // 폴링 주기 (저장된 값 즉시 반영)
     val pollingInterval: StateFlow<Int> = appSettings.pollingInterval
-        .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5000), 2)
+        .stateIn(viewModelScope, SharingStarted.Eagerly, 2)
     
     init {
         initializeApp()