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/shared/utils/room_preview.dart

@@ -1,4 +1,4 @@
-// Version: 1.1.0 | Created: 2026-04-02 | Updated: 2026-04-10
+// Version: 1.1.1 | Created: 2026-04-02 | Updated: 2026-07-03
 // Shared utility for generating a last-message preview string from a Room.
 // Used by both RoomsRepository and SyncPersistenceService to avoid duplication.
 
@@ -12,7 +12,7 @@ String? lastMessagePreview(Room room) {
 
   return switch (lastEvent.type) {
     EventTypes.Message => lastEvent.body,
-    EventTypes.Encrypted => '\u{1F512} Encrypted — use Element to read',
+    EventTypes.Encrypted => '\u{1F512} Encrypted. Use Element to read',
     EventTypes.Sticker => 'Sticker',
     _ => null,
   };