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/server/src/ws/events.ts

@@ -141,6 +141,9 @@ export function handleClientEvent(
     case 'reaction_remove':
       handleReactionRemove(event, userId);
       break;
+    case 'channel_ack':
+      handleChannelAck(event, userId);
+      break;
     default:
       connectionManager.sendToUser(userId, {
         type: 'error',
@@ -677,3 +680,48 @@ function handleReactionRemove(event: Record<string, unknown>, userId: string): v
     });
   }
 }
+
+function handleChannelAck(event: Record<string, unknown>, userId: string): void {
+  const channelId = event.channelId as string;
+  const messageId = event.messageId as string;
+  if (!channelId || !messageId) return;
+
+  const db = getDb();
+
+  const existing = db.select()
+    .from(schema.readStates)
+    .where(and(
+      eq(schema.readStates.userId, userId),
+      eq(schema.readStates.channelId, channelId),
+    ))
+    .get();
+
+  const now = Date.now();
+
+  if (existing) {
+    // Only update if the new messageId is newer (larger snowflake)
+    if (BigInt(messageId) > BigInt(existing.lastReadMessageId)) {
+      db.update(schema.readStates)
+        .set({ lastReadMessageId: messageId, updatedAt: now })
+        .where(and(
+          eq(schema.readStates.userId, userId),
+          eq(schema.readStates.channelId, channelId),
+        ))
+        .run();
+    }
+  } else {
+    db.insert(schema.readStates).values({
+      userId,
+      channelId,
+      lastReadMessageId: messageId,
+      updatedAt: now,
+    }).run();
+  }
+
+  // Echo ack back to all of this user's connections (multi-tab sync)
+  connectionManager.sendToUser(userId, {
+    type: 'channel_ack',
+    channelId,
+    messageId,
+  });
+}