feat: add search and filter support to chats endpoint (#25391)

Fixes https://linear.app/codercom/issue/CODAGT-432

Adds structured search/filter capabilities to the `GET
/api/experimental/chats/` endpoint via the `q` query parameter. All
filters use explicit `key:value` syntax; bare terms are rejected to
reserve them for potential future full-text search.

> Generated by Coder Agents

Co-authored-by: Danielle Maywood <danielle@themaywoods.com>
Co-authored-by: Jaayden Halko <jaayden.halko@gmail.com>

coderd/database/modelqueries.go

@@ -775,6 +775,9 @@ func (q *sqlQuerier) GetAuthorizedChats(ctx context.Context, arg GetChatsParams,
 		arg.AfterID,
 		arg.LabelFilter,
 		arg.DiffURL,
+		arg.TitleQuery,
+		arg.HasUnread,
+		pq.Array(arg.PullRequestStatuses),
 		arg.OffsetOpt,
 		arg.LimitOpt,
 	)