feat(#97): Share logs / Open logs folder action on the debug log screen

Platform-adaptive export on the BLE/frame log screen: the system share sheet on
mobile (the priority path), or open the logs folder in the file manager on
desktop. Web-safe (defaultTargetPlatform, no dart:io); flushes the file first so
it is current. Completes #97.

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

lib/screens/ble_debug_log_screen.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:flutter/foundation.dart';
 import 'package:provider/provider.dart';
 import 'package:flutter/services.dart';
 import '../l10n/l10n.dart';
@@ -6,6 +7,9 @@ import '../services/ble_debug_log_service.dart';
 import '../connector/meshcore_protocol.dart';
 import '../widgets/adaptive_app_bar_title.dart';
 import '../helpers/snack_bar_builder.dart';
+import 'package:share_plus/share_plus.dart';
+import 'package:url_launcher/url_launcher.dart';
+import '../services/file_log_service.dart';
 
 enum _BleLogView { frames, rawLogRx }
 
@@ -29,10 +33,18 @@ class _BleDebugLogScreenState extends State<BleDebugLogScreen> {
         final hasEntries = showingFrames
             ? entries.isNotEmpty
             : rawEntries.isNotEmpty;
+        final isMobile =
+            defaultTargetPlatform == TargetPlatform.android ||
+            defaultTargetPlatform == TargetPlatform.iOS;
         return Scaffold(
           appBar: AppBar(
             title: AdaptiveAppBarTitle(context.l10n.debugLog_bleTitle),
             actions: [
+              IconButton(
+                tooltip: isMobile ? 'Share logs' : 'Open logs folder',
+                icon: Icon(isMobile ? Icons.ios_share : Icons.folder_open),
+                onPressed: () => _exportLogs(context),
+              ),
               IconButton(
                 tooltip: context.l10n.debugLog_copyLog,
                 icon: const Icon(Icons.copy),
@@ -160,6 +172,36 @@ class _BleDebugLogScreenState extends State<BleDebugLogScreen> {
     );
   }
 
+  /// Export the on-disk log (#97): the system share sheet on mobile, or open the
+  /// logs folder in the file manager on desktop. The file holds both the app log
+  /// and BLE frames, flushed first so it's current.
+  Future<void> _exportLogs(BuildContext context) async {
+    final messenger = ScaffoldMessenger.of(context);
+    final file = await FileLogService.instance.flushAndGetActiveFile();
+    if (file == null) {
+      messenger.showSnackBar(
+        const SnackBar(
+          content: Text('File logging is unavailable on this platform'),
+        ),
+      );
+      return;
+    }
+    final isMobile =
+        defaultTargetPlatform == TargetPlatform.android ||
+        defaultTargetPlatform == TargetPlatform.iOS;
+    if (isMobile) {
+      await SharePlus.instance.share(
+        ShareParams(
+          subject: 'Offband Meshcore logs',
+          files: [XFile(file.path)],
+        ),
+      );
+    } else {
+      final dir = FileLogService.instance.logDir;
+      if (dir != null) await launchUrl(Uri.file(dir.path));
+    }
+  }
+
   void _showRawDialog(BuildContext context, _RawPacketInfo info) {
     showDialog(
       context: context,