feat: brand retheme to m8chat.au blues, fix black logo, v1.6.0+8

- m8logo.svg: inline fills (flutter_svg ignores <style> blocks; logo rendered black)
- theme.dart v2.0.0: purple -> site palette (#1265ED / #3B8BFF / navy darks)
- app_config.dart: appVersion 1.3.0 -> 1.6.0 (profile screen showed stale version)
- manifest.json: theme/background colours to match
- Remove em-dashes from user-visible UI strings (global style rule)
- chat_screen.dart: fix use_build_context_synchronously in _leaveRoom
- Deployed to app2.m8chat.au after full functionality audit (all green)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/features/chat/presentation/message_bubble.dart

@@ -1,4 +1,4 @@
-// Version: 1.3.0 | Created: 2026-04-01 | Updated: 2026-04-27
+// Version: 1.3.1 | Created: 2026-04-01 | Updated: 2026-07-03
 // Message bubble widget. Handles text, images, files, redacted, replies.
 
 import 'package:cached_network_image/cached_network_image.dart';
@@ -145,7 +145,7 @@ class _MessageContentBody extends StatelessWidget {
           const SizedBox(width: 6),
           Flexible(
             child: Text(
-              'Encrypted — use Element to read',
+              'Encrypted. Use Element to read',
               style: TextStyle(
                 color: textColour.withAlpha(153),
                 fontStyle: FontStyle.italic,