feat(alarmas): replace one-line reliability button with full diagnostics screen

Surface all six DiagnosticoAlarmasAndroid fields instead of three: the
battery-optimization exemption and native pending-alarm count were
already collected but silently dropped by the old widget. Each failing
signal now offers a "Fix this" action that opens the right system
settings screen (exact alarms, notifications, full-screen intent,
battery optimization), guarded by SDK level and never crashing when a
ROM lacks that screen. Manufacturers known for aggressive background
killing (Xiaomi/Redmi/POCO, Huawei, Oppo, Vivo, OnePlus, Samsung) get
an honest explanation that Autostart must be enabled manually, since
there is no API to detect or grant it.

Notifications now deep-links straight to
ACTION_APP_NOTIFICATION_SETTINGS via a new openNotificationSettings
native method, instead of reusing the runtime permission popup meant
for first-time alarm creation.

New copy is added to all 13 ARB locales with real per-language
translations (not Spanish copies), verified by the ARB parity and
anti-copy tests plus the corruption scanner.

lib/l10n/gen/app_localizations_en.dart

@@ -1692,4 +1692,74 @@ class AppLocalizationsEn extends AppLocalizations {
 
   @override
   String get alarmCardVacationPausedBadge => 'Paused for vacation';
+
+  @override
+  String get alarmDiagnosticsExactAlarmsTitle => 'Exact alarm scheduling';
+
+  @override
+  String get alarmDiagnosticsExactAlarmsHint =>
+      'Lets the alarm ring at the exact minute you set, even while the phone is asleep.';
+
+  @override
+  String get alarmDiagnosticsNotificationsTitle => 'Notifications';
+
+  @override
+  String get alarmDiagnosticsNotificationsHint =>
+      'Needed to show the alarm and the advance-warning notice.';
+
+  @override
+  String get alarmDiagnosticsFullScreenTitle => 'Full-screen alarm display';
+
+  @override
+  String get alarmDiagnosticsFullScreenHint =>
+      'Lets the ringing screen appear automatically, even with the phone locked.';
+
+  @override
+  String get alarmDiagnosticsBatteryTitle => 'Battery optimization';
+
+  @override
+  String get alarmDiagnosticsBatteryHint =>
+      'Stops the system from closing PluriWave in the background so the alarm can still fire.';
+
+  @override
+  String get alarmDiagnosticsNativeCountTitle =>
+      'Alarms registered with Android';
+
+  @override
+  String alarmDiagnosticsNativeCountValue(int count) {
+    return 'Currently registered: $count';
+  }
+
+  @override
+  String get alarmDiagnosticsNativeCountAttentionHint =>
+      'You have an alarm turned on, but none are registered with the system yet. Reopen PluriWave, or fix the items above first.';
+
+  @override
+  String get alarmDiagnosticsManufacturerLabel => 'Manufacturer';
+
+  @override
+  String get alarmDiagnosticsSdkLabel => 'Android version (SDK)';
+
+  @override
+  String get alarmDiagnosticsNeedsAttentionStatus => 'Needs attention';
+
+  @override
+  String get alarmDiagnosticsAutostartTitle =>
+      'One more manual step on this phone';
+
+  @override
+  String alarmDiagnosticsAutostartBody(String manufacturer) {
+    return '$manufacturer phones often close apps running in the background to save battery. There is no setting PluriWave can switch on its own — you need to turn on Autostart (sometimes called \"Auto-start\" or \"Background activity\") for PluriWave yourself. Look in Settings, under Apps or Battery, or in the phone\'s own Security app.';
+  }
+
+  @override
+  String get alarmDiagnosticsFixAction => 'Fix this';
+
+  @override
+  String get alarmDiagnosticsIntentUnavailable =>
+      'Couldn\'t open that settings screen on this phone. Try looking for it manually in Settings.';
+
+  @override
+  String get alarmDiagnosticsUnavailableHint =>
+      'We couldn\'t check your alarm settings yet.';
 }