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/modals/UserSettings.tsx

@@ -67,10 +67,10 @@ export function UserSettingsModal() {
         </div>
 
         {error && (
-          <div className="p-2 bg-discord-red/10 border border-discord-red/30 rounded text-discord-red text-sm">{error}</div>
+          <div className="p-2 bg-discord-red/10 border border-discord-red/30 rounded text-discord-text-danger text-sm">{error}</div>
         )}
         {success && (
-          <div className="p-2 bg-discord-green/10 border border-discord-green/30 rounded text-discord-green text-sm">{success}</div>
+          <div className="p-2 bg-discord-green/10 border border-discord-green/30 rounded text-discord-text-positive text-sm">{success}</div>
         )}
 
         <div>