chore: remove swagger annotations from experimental chat endpoints (#23120)

The `/archive` and `/desktop` chat endpoints had swagger route comments
(`@Summary`, `@ID`, `@Router`, etc.) that would cause them to appear in
generated API docs. Since these live under `/experimental/chats`, they
should not be documented.

This removes the swagger annotations and adds the standard `//
EXPERIMENTAL: this endpoint is experimental and is subject to change.`
comment to `archiveChat` (the `watchChatDesktop` handler already had it,
just needed the swagger block removed).

docs/manifest.json

@@ -1416,10 +1416,6 @@
 							"title": "Builds",
 							"path": "./reference/api/builds.md"
 						},
-						{
-							"title": "Chats",
-							"path": "./reference/api/chats.md"
-						},
 						{
 							"title": "Debug",
 							"path": "./reference/api/debug.md"