Change polling interval to retrieve BusiLight status (#3)

Implement a more agressive polling interval to retrieve BusiLight status.
From (in sec.):
```
- min: 0
- max: 60
- default: 5
- divisions: 12
```
to (in sec.):
```
- min: 0
- max: 2
- default: 1
- divisions: 4
```

Reviewed-on: #3

lib/providers/busylight_provider.dart

@@ -10,7 +10,7 @@ import '../services/busylight_service.dart';
 const _kHostKey        = 'busylight_host';
 const _kDefaultHost    = 'http://igox-busylight.local';
 const _kPollIntervalKey     = 'busylight_poll_interval';
-const _kDefaultPollInterval = 5; // seconds
+const _kDefaultPollInterval = 1.0; // seconds
 
 final sharedPreferencesProvider = FutureProvider<SharedPreferences>(
   (_) => SharedPreferences.getInstance(),
@@ -21,9 +21,9 @@ final deviceHostProvider = StateProvider<String>((ref) {
   return prefs?.getString(_kHostKey) ?? _kDefaultHost;
 });
 
-final pollIntervalProvider = StateProvider<int>((ref) {
+final pollIntervalProvider = StateProvider<double>((ref) {
   final prefs = ref.watch(sharedPreferencesProvider).valueOrNull;
-  return prefs?.getInt(_kPollIntervalKey) ?? _kDefaultPollInterval;
+  return prefs?.getDouble(_kPollIntervalKey) ?? _kDefaultPollInterval.toDouble();
 });
 
 // ── Service ──────────────────────────────────────────────────────────────────
@@ -161,10 +161,11 @@ class PollingNotifier extends StateNotifier<void> {
   Timer? _timer;
 
   void _start() {
-    final interval = _ref.read(pollIntervalProvider);
+    final intervalSeconds = _ref.read(pollIntervalProvider);
+    final intervalMillis = (intervalSeconds * 1000).toInt();
     _timer?.cancel();
-    if (interval <= 0) return;
-    _timer = Timer.periodic(Duration(seconds: interval), (_) => _poll());
+    if (intervalMillis <= 0) return;
+    _timer = Timer.periodic(Duration(milliseconds: intervalMillis), (_) => _poll());
   }
 
   void restart() => _start();