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>

web/manifest.json

@@ -3,8 +3,8 @@
     "short_name": "M8Chat",
     "start_url": ".",
     "display": "standalone",
-    "background_color": "#0F0F1A",
-    "theme_color": "#5C35C9",
+    "background_color": "#0A0F2E",
+    "theme_color": "#1265ED",
     "description": "M8Chat — secure chat and conferencing.",
     "orientation": "portrait-primary",
     "prefer_related_applications": false,