feat: background update download, snackbar prompt, chat image rendering

Update provider: auto-downloads APK in background after finding a newer
version, prompts via snackbar only when ready, cleans up old APKs on
startup. Replaces modal dialog with dismissible snackbar.

Chat bubble: resolve relative image URLs (/api/images/{id}) against
server base URL with auth cookies so search_images results render on
the phone app.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/widgets/chat_message_bubble.dart

@@ -1,12 +1,17 @@
 import 'dart:math' show min;
+import 'dart:typed_data';
 
+import 'package:dio/dio.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_markdown_plus/flutter_markdown_plus.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
 
 import '../data/models/message.dart';
+import '../providers/api_client_provider.dart';
+import '../providers/settings_provider.dart';
 import 'tool_call_chip.dart';
 
-class ChatMessageBubble extends StatelessWidget {
+class ChatMessageBubble extends ConsumerWidget {
   final Message message;
   final String streamingStatus;
   const ChatMessageBubble({
@@ -16,9 +21,11 @@ class ChatMessageBubble extends StatelessWidget {
   });
 
   @override
-  Widget build(BuildContext context) {
+  Widget build(BuildContext context, WidgetRef ref) {
     final isUser = message.role == MessageRole.user;
     final scheme = Theme.of(context).colorScheme;
+    final serverUrl = ref.watch(serverUrlProvider) ?? '';
+    final dio = ref.watch(dioProvider);
     final isGenerating = message.status == 'generating';
     final toolCalls = message.toolCalls ?? const [];
 
@@ -116,6 +123,14 @@ class ChatMessageBubble extends StatelessWidget {
                     if (message.content.isNotEmpty)
                       MarkdownBody(
                         data: message.content,
+                        imageBuilder: (uri, title, alt) {
+                          return _AuthImage(
+                            uri: uri,
+                            alt: alt,
+                            serverUrl: serverUrl,
+                            dio: dio,
+                          );
+                        },
                         styleSheet: MarkdownStyleSheet(
                           p: TextStyle(
                             color: isUser
@@ -161,3 +176,69 @@ class ChatMessageBubble extends StatelessWidget {
     );
   }
 }
+
+class _AuthImage extends StatefulWidget {
+  final Uri uri;
+  final String? alt;
+  final String serverUrl;
+  final Dio dio;
+
+  const _AuthImage({
+    required this.uri,
+    this.alt,
+    required this.serverUrl,
+    required this.dio,
+  });
+
+  @override
+  State<_AuthImage> createState() => _AuthImageState();
+}
+
+class _AuthImageState extends State<_AuthImage> {
+  late Future<Uint8List> _future;
+
+  @override
+  void initState() {
+    super.initState();
+    _future = _fetchImage();
+  }
+
+  Future<Uint8List> _fetchImage() async {
+    var url = widget.uri.toString();
+    if (url.startsWith('/')) {
+      url = '${widget.serverUrl}$url';
+    }
+    final response = await widget.dio.get<List<int>>(
+      url,
+      options: Options(responseType: ResponseType.bytes),
+    );
+    return Uint8List.fromList(response.data!);
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return FutureBuilder<Uint8List>(
+      future: _future,
+      builder: (context, snapshot) {
+        if (snapshot.connectionState == ConnectionState.waiting) {
+          return const SizedBox(
+            height: 100,
+            child: Center(child: CircularProgressIndicator(strokeWidth: 2)),
+          );
+        }
+        if (snapshot.hasError || !snapshot.hasData) {
+          return Text(widget.alt ?? 'Image failed to load');
+        }
+        return ClipRRect(
+          borderRadius: BorderRadius.circular(8),
+          child: Image.memory(
+            snapshot.data!,
+            fit: BoxFit.contain,
+            errorBuilder: (_, _, _) =>
+                Text(widget.alt ?? 'Image failed to load'),
+          ),
+        );
+      },
+    );
+  }
+}