feat: unread indicators + DM bug fixes + data-driven isDmChannel

- Fix stale message cache: add force param to loadMessages, clearAllMessages action
- Fix reload race condition: URL-based isDmChannel fallback before WS ready
- Add read_states DB table for persistent unread tracking
- Add channel_ack WS event (client→server→echo) with BigInt comparison
- Wire up unread state in chatStore (readStates, unreadChannels, ackChannel)
- Auto-ack channels on MessageList view (200ms debounced)
- Unread pill indicators on server icons in ServerSidebar
- Bold text + white dot on unread channels/DMs in ChannelSidebar
- Replace all showDms reads with data-driven isDmChannel() across 8 files
- Design system, UI polish, and component fixes from previous sessions

packages/web/src/components/voice/VoiceChannel.tsx

@@ -41,7 +41,7 @@ export function VoiceChannel({ channelId, channelName, onClick }: VoiceChannelPr
             if (!member) return null;
             const displayName = member.user.displayName ?? member.user.username;
             return (
-              <div key={userId} className="flex items-center gap-2 px-2 py-0.5 rounded hover:bg-discord-bg-hover">
+              <div key={userId} className="flex items-center gap-2 px-2 py-0.5 rounded hover:bg-discord-bg-hover transition-colors">
                 <Avatar
                   src={member.user.avatar}
                   name={displayName}