fix(#443): guard battery-optimization platform calls (Gemini review)

Gemini flagged two unhandled PlatformException paths (SAFELANE §6):
- isIgnoringBatteryOptimizations could throw -> banner silently never shows;
  now caught + logged, leaving the banner hidden on an unknown status.
- openIgnoreBatteryOptimizationSettings could throw -> button did nothing with
  no feedback; now caught + logged + a snackbar tells the user it failed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/l10n/app_en.arb

@@ -2683,5 +2683,9 @@
   "batteryOptimizationDismiss": "Dismiss",
   "@batteryOptimizationDismiss": {
     "description": "Tooltip for the button that hides the battery-optimization banner for this session (#443)."
+  },
+  "batteryOptimizationOpenFailed": "Couldn't open battery settings",
+  "@batteryOptimizationOpenFailed": {
+    "description": "Snackbar shown when the battery-optimization settings screen could not be opened (#443)."
   }
 }

lib/l10n/app_localizations.dart

@@ -8079,6 +8079,12 @@ abstract class AppLocalizations {
   /// In en, this message translates to:
   /// **'Dismiss'**
   String get batteryOptimizationDismiss;
+
+  /// Snackbar shown when the battery-optimization settings screen could not be opened (#443).
+  ///
+  /// In en, this message translates to:
+  /// **'Couldn\'t open battery settings'**
+  String get batteryOptimizationOpenFailed;
 }
 
 class _AppLocalizationsDelegate

lib/l10n/app_localizations_bg.dart

@@ -4726,4 +4726,7 @@ class AppLocalizationsBg extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/l10n/app_localizations_de.dart

@@ -4743,4 +4743,7 @@ class AppLocalizationsDe extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/l10n/app_localizations_en.dart

@@ -4648,4 +4648,7 @@ class AppLocalizationsEn extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/l10n/app_localizations_es.dart

@@ -4731,4 +4731,7 @@ class AppLocalizationsEs extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/l10n/app_localizations_fr.dart

@@ -4759,4 +4759,7 @@ class AppLocalizationsFr extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/l10n/app_localizations_hu.dart

@@ -4748,4 +4748,7 @@ class AppLocalizationsHu extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/l10n/app_localizations_it.dart

@@ -4736,4 +4736,7 @@ class AppLocalizationsIt extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/l10n/app_localizations_ja.dart

@@ -4502,4 +4502,7 @@ class AppLocalizationsJa extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/l10n/app_localizations_ko.dart

@@ -4503,4 +4503,7 @@ class AppLocalizationsKo extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/l10n/app_localizations_nl.dart

@@ -4711,4 +4711,7 @@ class AppLocalizationsNl extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/l10n/app_localizations_pl.dart

@@ -4748,4 +4748,7 @@ class AppLocalizationsPl extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/l10n/app_localizations_pt.dart

@@ -4724,4 +4724,7 @@ class AppLocalizationsPt extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/l10n/app_localizations_ru.dart

@@ -4742,4 +4742,7 @@ class AppLocalizationsRu extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/l10n/app_localizations_sk.dart

@@ -4708,4 +4708,7 @@ class AppLocalizationsSk extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/l10n/app_localizations_sl.dart

@@ -4706,4 +4706,7 @@ class AppLocalizationsSl extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/l10n/app_localizations_sv.dart

@@ -4681,4 +4681,7 @@ class AppLocalizationsSv extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/l10n/app_localizations_uk.dart

@@ -4743,4 +4743,7 @@ class AppLocalizationsUk extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/l10n/app_localizations_zh.dart

@@ -4376,4 +4376,7 @@ class AppLocalizationsZh extends AppLocalizations {
 
   @override
   String get batteryOptimizationDismiss => 'Dismiss';
+
+  @override
+  String get batteryOptimizationOpenFailed => 'Couldn\'t open battery settings';
 }

lib/widgets/battery_optimization_banner.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_foreground_task/flutter_foreground_task.dart';
 
 import '../l10n/l10n.dart';
+import '../utils/app_logger.dart';
 import '../utils/platform_info.dart';
 
 /// Warns the user when the app is NOT exempt from Android battery optimization
@@ -58,15 +59,36 @@ class _BatteryOptimizationBannerState extends State<BatteryOptimizationBanner>
 
   Future<void> _check() async {
     if (!PlatformInfo.isAndroid) return;
-    final ignoring = await FlutterForegroundTask.isIgnoringBatteryOptimizations;
+    try {
+      final ignoring =
+          await FlutterForegroundTask.isIgnoringBatteryOptimizations;
       if (!mounted) return;
       setState(() => _ignoring = ignoring);
+    } catch (e) {
+      // Can't confirm the status — leave the banner hidden rather than risk a
+      // false warning, but surface the failure to the log (SAFELANE §6).
+      appLogger.warn(
+        'Battery-optimization status check failed: $e',
+        tag: 'BatteryBanner',
+      );
+    }
   }
 
   Future<void> _openSettings() async {
+    try {
       await FlutterForegroundTask.openIgnoreBatteryOptimizationSettings();
       // The user returns via resume, which triggers _check() and clears the
       // banner if they applied the change.
+    } catch (e) {
+      appLogger.warn(
+        'Failed to open battery-optimization settings: $e',
+        tag: 'BatteryBanner',
+      );
+      if (!mounted) return;
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(content: Text(context.l10n.batteryOptimizationOpenFailed)),
+      );
+    }
   }
 
   @override