fix(coderd/x/chatd): forward local status events to fix delayed-startup banner (#23650)

## Problem

The agent chat delayed-startup banner ("Response startup is taking
longer than expected") could appear even though the model was already
streaming.

The root cause is in `Subscribe()`: `message_part` events were delivered
via the fast local in-process stream, while `status` events were
delivered via PostgreSQL pubsub. Both feed into the same `select`
statement, and Go's `select` picks whichever channel is ready first —
there is no ordering guarantee between channels. So a `message_part`
could outrun the `status=running` that logically precedes it.

The frontend saw content arrive while it still thought the chat was
pending, triggering the banner.

## Fix

Also forward `status` events from the local channel, alongside
`message_part`.

Both event types already travel through the same FIFO subscriber
channel: `publishStatus()` is called before the first `message_part`, so
channel ordering guarantees the frontend sees `status=running` before
any content.

Pubsub still delivers a duplicate `status` event later; the frontend
deduplicates it (`setChatStatus` is idempotent — it early-returns when
the status hasn't changed).

coderd/x/chatd/chatd.go

@@ -2871,9 +2871,20 @@ func (p *Server) Subscribe(
 					continue
 				}
 				if hasPubsub {
-					// Only forward message_part events from local
-					// (durable events come via pubsub + cache).
-					if event.Type == codersdk.ChatStreamEventTypeMessagePart {
+					// Forward transient events from local.
+					// Durable events (messages, queue updates)
+					// come via pubsub + cache.  Status is
+					// included alongside message_part because
+					// both travel through the same ordered
+					// channel: publishStatus is called before
+					// the first message_part, so FIFO delivery
+					// guarantees the frontend sees
+					// status=running before any content.
+					// Pubsub will deliver a duplicate status
+					// later; the frontend deduplicates it
+					// (setChatStatus is idempotent).
+					if event.Type == codersdk.ChatStreamEventTypeMessagePart ||
+						event.Type == codersdk.ChatStreamEventTypeStatus {
 						select {
 						case <-mergedCtx.Done():
 							return