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/spaces.ts

@@ -508,8 +508,12 @@ export async function spaceRoutes(app: FastifyInstance): Promise<void> {
     const spaceIcon = server.icon;
     const spaceBanner = server.banner;
 
-    // Delete all channels (messages cascade), members, folder refs, then space atomically
+    // Delete all channels (messages cascade), members, folder refs, read states, then space atomically
     db.transaction((tx) => {
+      // Clean up read_states for all channels in this space (no FK cascade — channelId is plain text)
+      if (channelIds.length > 0) {
+        tx.delete(schema.readStates).where(inArray(schema.readStates.channelId, channelIds)).run();
+      }
       tx.delete(schema.channels).where(eq(schema.channels.spaceId, id)).run();
       tx.delete(schema.spaceMembers).where(eq(schema.spaceMembers.spaceId, id)).run();
       tx.delete(schema.spaceFolderMembers).where(eq(schema.spaceFolderMembers.spaceId, id)).run();
@@ -941,6 +945,16 @@ export async function spaceRoutes(app: FastifyInstance): Promise<void> {
       )
     ).run();
 
+    // Clean up read_states for the departing user in this space's channels
+    const spaceChannelIds = db.select({ id: schema.channels.id })
+      .from(schema.channels).where(eq(schema.channels.spaceId, id)).all().map(c => c.id);
+    if (spaceChannelIds.length > 0) {
+      db.delete(schema.readStates).where(and(
+        eq(schema.readStates.userId, uid),
+        inArray(schema.readStates.channelId, spaceChannelIds),
+      )).run();
+    }
+
     // Broadcast member_left event
     connectionManager.sendToSpace(id, {
       type: 'member_left',
@@ -1269,6 +1283,10 @@ export async function spaceRoutes(app: FastifyInstance): Promise<void> {
 
     const now = Date.now();
 
+    // Fetch channel IDs before the transaction for read_states cleanup
+    const banChannelIds = db.select({ id: schema.channels.id })
+      .from(schema.channels).where(eq(schema.channels.spaceId, id)).all().map(c => c.id);
+
     db.transaction((tx) => {
       // Insert ban record
       tx.insert(schema.bans).values({
@@ -1291,6 +1309,14 @@ export async function spaceRoutes(app: FastifyInstance): Promise<void> {
         eq(schema.memberRoles.userId, targetId),
       )).run();
 
+      // Clean up read_states for the banned user in this space's channels
+      if (banChannelIds.length > 0) {
+        tx.delete(schema.readStates).where(and(
+          eq(schema.readStates.userId, targetId),
+          inArray(schema.readStates.channelId, banChannelIds),
+        )).run();
+      }
+
       // Clean up any voice restrictions for the banned member
       tx.delete(schema.voiceRestrictions).where(and(
         eq(schema.voiceRestrictions.spaceId, id),