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/schema.ts

@@ -138,6 +138,15 @@ export const memberRoles = sqliteTable('member_roles', {
   pk: primaryKey({ columns: [table.serverId, table.userId, table.roleId] }),
 }));
 
+export const readStates = sqliteTable('read_states', {
+  userId: text('user_id').notNull().references(() => users.id, { onDelete: 'cascade' }),
+  channelId: text('channel_id').notNull(),
+  lastReadMessageId: text('last_read_message_id').notNull(),
+  updatedAt: integer('updated_at').notNull(),
+}, (table) => ({
+  pk: primaryKey({ columns: [table.userId, table.channelId] }),
+}));
+
 export const serverFolders = sqliteTable('server_folders', {
   id: text('id').primaryKey(),
   userId: text('user_id').notNull().references(() => users.id, { onDelete: 'cascade' }),