fix: add archived query parameter to chat list endpoint (#22562)

Despite the SDK type having an `Archived` field for chats, this data was
never fetched from the database — the `GetChatsByOwnerID` query
hardcoded `AND archived = false`, and the `convertChat` function never
mapped the field.

This PR adds an optional `archived` query parameter to `GET
/api/experimental/chats`:

| Value | Behavior |
|-------|----------|
| *(not provided)* | Returns all chats (active and archived) |
| `archived=false` | Returns only non-archived chats |
| `archived=true` | Returns only archived chats |

This follows the same pattern used by template versions
(`sqlc.narg('archived')` nullable boolean).

Also fixes `convertChat` to populate the `Archived` field in API
responses, which was never being set despite existing on the SDK type.

site/src/api/typesGenerated.ts

@@ -3216,6 +3216,14 @@ export interface LinkConfig {
 	readonly location?: string;
 }
 
+// From codersdk/chats.go
+/**
+ * ListChatsOptions are optional parameters for ListChats.
+ */
+export interface ListChatsOptions {
+	readonly Archived: boolean | null;
+}
+
 // From codersdk/inboxnotification.go
 export interface ListInboxNotificationsRequest {
 	readonly targets?: string;