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/db/index.ts

@@ -143,6 +143,14 @@ function createTables(db: Database.Database): void {
       PRIMARY KEY (server_id, user_id, role_id)
     );
 
+    CREATE TABLE IF NOT EXISTS read_states (
+      user_id TEXT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+      channel_id TEXT NOT NULL,
+      last_read_message_id TEXT NOT NULL,
+      updated_at INTEGER NOT NULL,
+      PRIMARY KEY (user_id, channel_id)
+    );
+
     CREATE TABLE IF NOT EXISTS server_folders (
       id TEXT PRIMARY KEY,
       user_id TEXT NOT NULL REFERENCES users(id) ON DELETE CASCADE,