fix: eliminate phantom notifications across the entire read-state pipeline

Root cause: own messages echoed by the server marked channels unread when
the user had already navigated away. Seven related bugs compounded the
problem — stale read states, missing cleanup on space/DM removal, REST
broadcast ignoring VIEW_CHANNEL, and no validation on channel_ack writes.

Frontend:
- Skip markChannelUnread for the user's own messages (federation-aware)
- Walk backward past temp_ IDs in ackChannel instead of bailing
- Re-fire ack timer when temp message is replaced by server-confirmed ID
- Add removeChannelStates to clean up unread/read/message caches
- Clean up chatStore on removeSpace, removeDmChannel, removeInstanceSpaces

Server:
- Use sendToChannel instead of sendToSpace for REST message creation
- Clean up read_states on space deletion, member kick/leave, and ban
- Validate channel membership before accepting channel_ack writes
- Clean up read_states on DM leave and DM channel deletion

packages/server/src/routes/messages.ts

@@ -343,7 +343,7 @@ export async function messageRoutes(app: FastifyInstance): Promise<void> {
     const messageWithUser = buildMessageWithUser(message, user, attachmentRows, [], replyTo);
 
     // Broadcast via WebSocket
-    connectionManager.sendToSpace(spaceId, {
+    connectionManager.sendToChannel(spaceId, id, {
       type: 'message_created',
       message: messageWithUser,
     });