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/main.tsx

@@ -26,13 +26,13 @@ class ErrorBoundary extends React.Component<
           alignItems: 'center',
           justifyContent: 'center',
           backgroundColor: '#313338',
-          color: '#f2f3f5',
+          color: '#ffffff',
           fontFamily: 'sans-serif',
           flexDirection: 'column',
           gap: '16px',
         }}>
           <h1 style={{ fontSize: '24px', fontWeight: 'bold' }}>Something went wrong</h1>
-          <p style={{ color: '#949ba4' }}>{this.state.error?.message}</p>
+          <p style={{ color: '#abacb2' }}>{this.state.error?.message}</p>
           <button
             onClick={() => window.location.reload()}
             style={{