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/chat/FriendsPage.tsx

@@ -160,7 +160,7 @@ export function FriendsPage() {
               </button>
             </form>
             {addStatus && (
-              <div className={`text-sm p-3 rounded-lg border ${addStatus.type === 'success' ? 'text-discord-green border-discord-green/20 bg-discord-green/5' : 'text-discord-red border-discord-red/20 bg-discord-red/5'}`}>
+              <div className={`text-sm p-3 rounded-lg border ${addStatus.type === 'success' ? 'text-discord-text-positive border-discord-green/20 bg-discord-green/5' : 'text-discord-text-danger border-discord-red/20 bg-discord-red/5'}`}>
                 {addStatus.message}
               </div>
             )}