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/help/presentation/help_tab.dart

@@ -1,4 +1,4 @@
-// Version: 1.1.0 | Created: 2026-04-11 | Updated: 2026-04-11
+// Version: 1.1.1 | Created: 2026-04-11 | Updated: 2026-07-03
 // Help tab with in-app guidance for common tasks and troubleshooting.
 
 import 'package:flutter/material.dart';
@@ -36,7 +36,7 @@ class HelpTab extends ConsumerWidget {
         // --- Encrypted messages ---
         _HelpCard(
           icon: Icons.lock_outline,
-          title: 'I see "Encrypted — use Element to read"',
+          title: 'I see "Encrypted. Use Element to read"',
           children: [
             const _HelpParagraph(
               'This means your device does not have the keys needed to '
@@ -98,7 +98,7 @@ class HelpTab extends ConsumerWidget {
               '1. Set up security: go to Profile > Security & Privacy '
               '> Security setup. This creates your encryption keys and '
               'backs them up.\n'
-              '2. Save your recovery key — you will need it if you ever '
+              '2. Save your recovery key. You will need it if you ever '
               'log in on a new device.\n'
               '3. Start chatting. Tap the pencil icon at the top right '
               'to search for users and start a conversation.',
@@ -156,7 +156,7 @@ class HelpTab extends ConsumerWidget {
             _HelpSubheading('Who can read my messages?'),
             _HelpParagraph(
               'Only you and the people in the conversation. M8Chat uses '
-              'end-to-end encryption — not even the server operator can '
+              'end-to-end encryption. Not even the server operator can '
               'read your messages.',
             ),
             SizedBox(height: 8),