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/styles/globals.css

@@ -42,7 +42,7 @@
   input:-webkit-autofill,
   input:-webkit-autofill:hover,
   input:-webkit-autofill:focus {
-    -webkit-text-fill-color: #f2f3f5;
+    -webkit-text-fill-color: #ffffff;
     -webkit-box-shadow: 0 0 0px 1000px #1e1f22 inset;
     transition: background-color 5000s ease-in-out 0s;
   }
@@ -56,6 +56,15 @@
   .scrollbar-thin::-webkit-scrollbar {
     width: 4px;
   }
+
+  .scrollbar-thin::-webkit-scrollbar-track {
+    background: transparent;
+  }
+
+  .scrollbar-thin::-webkit-scrollbar-thumb {
+    background-color: rgba(255, 255, 255, 0.15);
+    border-radius: 100px;
+  }
 }
 
 /* Animations */