fix(coderd): unarchive child chats with parents (#23761)

Unarchiving a root chat now restores descendant chats in the database
and emits lifecycle events for every affected chat so passive sessions
converge without a full refetch.

This keeps archive and unarchive symmetric at both the data and
watch-stream layers by returning the affected chat family from the
database, using those post-update rows for chatd pubsub fanout, and
covering descendant lifecycle delivery with a watch-level regression
test.

Closes #23666

coderd/database/queries/chats.sql

@@ -1,9 +1,24 @@
--- name: ArchiveChatByID :exec
-UPDATE chats SET archived = true, pin_order = 0, updated_at = NOW()
-WHERE id = @id OR root_chat_id = @id;
+-- name: ArchiveChatByID :many
+WITH chats AS (
+    UPDATE chats
+    SET archived = true, pin_order = 0, updated_at = NOW()
+    WHERE id = @id::uuid OR root_chat_id = @id::uuid
+    RETURNING *
+)
+SELECT *
+FROM chats
+ORDER BY (id = @id::uuid) DESC, created_at ASC, id ASC;
 
--- name: UnarchiveChatByID :exec
-UPDATE chats SET archived = false, updated_at = NOW() WHERE id = @id::uuid;
+-- name: UnarchiveChatByID :many
+WITH chats AS (
+    UPDATE chats
+    SET archived = false, updated_at = NOW()
+    WHERE id = @id::uuid OR root_chat_id = @id::uuid
+    RETURNING *
+)
+SELECT *
+FROM chats
+ORDER BY (id = @id::uuid) DESC, created_at ASC, id ASC;
 
 -- name: PinChatByID :exec
 WITH target_chat AS (