feat: show remote-config launch announcement on app start

Introduce AppRemoteConfigService which fetches a platform/version/locale-aware JSON payload from api.zarz.moe/v1/spotiflac-mobile/config and caches it in SharedPreferences. main_shell shows a one-shot announcement dialog (respecting dismissible, CTA, time window and version gates) when no update prompt is pending; dismissed IDs are persisted so each announcement surfaces only once.

Tweaks bundled in: the service health dot loses its blur halo in favour of solid Material 3 tones, and AppInfo gains the remote config endpoint constant. The share listener and SAF migration hook stay synchronous inside the post-frame callback so share-intent URLs never race the network-bound checks.

New unit tests cover the announcement CTA/active-window rules.

lib/widgets/app_announcement_dialog.dart

@@ -0,0 +1,84 @@
+import 'package:flutter/material.dart';
+import 'package:url_launcher/url_launcher.dart';
+import 'package:spotiflac_android/services/app_remote_config_service.dart';
+
+class AppAnnouncementDialog extends StatelessWidget {
+  final RemoteAnnouncement announcement;
+  final VoidCallback onDismiss;
+
+  const AppAnnouncementDialog({
+    super.key,
+    required this.announcement,
+    required this.onDismiss,
+  });
+
+  Future<void> _openCta(BuildContext context) async {
+    final ctaUrl = announcement.ctaUrl;
+    if (ctaUrl == null || ctaUrl.isEmpty) return;
+
+    final uri = Uri.tryParse(ctaUrl);
+    if (uri == null) return;
+
+    await launchUrl(uri, mode: LaunchMode.externalApplication);
+    onDismiss();
+    if (context.mounted) {
+      Navigator.pop(context);
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final colorScheme = Theme.of(context).colorScheme;
+    final isUrgent = announcement.priority.toLowerCase() == 'high';
+
+    return AlertDialog(
+      icon: Icon(
+        isUrgent ? Icons.priority_high_rounded : Icons.campaign_rounded,
+        color: isUrgent ? colorScheme.error : colorScheme.primary,
+      ),
+      title: Text(announcement.title),
+      content: ConstrainedBox(
+        constraints: const BoxConstraints(maxHeight: 260),
+        child: SingleChildScrollView(
+          child: Text(
+            announcement.message,
+            style: Theme.of(
+              context,
+            ).textTheme.bodyMedium?.copyWith(height: 1.45),
+          ),
+        ),
+      ),
+      actions: [
+        TextButton(
+          onPressed: () {
+            onDismiss();
+            Navigator.pop(context);
+          },
+          child: Text(
+            announcement.dismissible
+                ? MaterialLocalizations.of(context).closeButtonLabel
+                : 'OK',
+          ),
+        ),
+        if (announcement.hasCta)
+          FilledButton(
+            onPressed: () => _openCta(context),
+            child: Text(announcement.ctaLabel!),
+          ),
+      ],
+    );
+  }
+}
+
+Future<void> showAppAnnouncementDialog(
+  BuildContext context, {
+  required RemoteAnnouncement announcement,
+  required VoidCallback onDismiss,
+}) {
+  return showDialog<void>(
+    context: context,
+    barrierDismissible: announcement.dismissible,
+    builder: (context) =>
+        AppAnnouncementDialog(announcement: announcement, onDismiss: onDismiss),
+  ).whenComplete(onDismiss);
+}

lib/widgets/download_service_picker.dart

@@ -78,7 +78,8 @@ class _DownloadServicePickerState extends ConsumerState<DownloadServicePicker> {
     });
     final downloadExtensions = _downloadExtensions();
     final recommended = widget.recommendedService;
-    if (recommended != null && _serviceExists(recommended, downloadExtensions)) {
+    if (recommended != null &&
+        _serviceExists(recommended, downloadExtensions)) {
       _selectedService = recommended;
     } else {
       _selectedService = ref.read(settingsProvider).defaultService;
@@ -383,17 +384,7 @@ class _ServiceHealthDot extends StatelessWidget {
       child: Container(
         width: 8,
         height: 8,
-        decoration: BoxDecoration(
-          color: color,
-          shape: BoxShape.circle,
-          boxShadow: [
-            BoxShadow(
-              color: color.withValues(alpha: 0.35),
-              blurRadius: 6,
-              spreadRadius: 1,
-            ),
-          ],
-        ),
+        decoration: BoxDecoration(color: color, shape: BoxShape.circle),
       ),
     );
   }
@@ -402,14 +393,14 @@ class _ServiceHealthDot extends StatelessWidget {
 Color _serviceHealthColor(String status) {
   switch (status) {
     case 'online':
-      return const Color(0xFF35D07F);
+      return const Color(0xFF24D47A);
     case 'degraded':
     case 'unknown':
-      return const Color(0xFFFFC857);
+      return const Color(0xFFFFC247);
     case 'offline':
-      return const Color(0xFFFF4D5E);
+      return const Color(0xFFFF5A66);
     default:
-      return const Color(0xFFFFC857);
+      return const Color(0xFFFFC247);
   }
 }