feat: add logout endpoint and users/me endpoint

- POST /api/v1/logout: deletes client token, returns {status: ok}
- GET /api/v1/users/me: returns session info (delegates to HandleState)
- Add DeleteClient, GetSessionCount, ClientCountForSession, DeleteStaleSessions to db layer
- Add user count to GET /api/v1/server response
- Extract setupAPIv1 to fix funlen lint issue

internal/server/routes.go

@@ -86,6 +86,14 @@ func (srv *Server) setupAPIv1(router chi.Router) {
 		"/state",
 		srv.handlers.HandleState(),
 	)
+	router.Post(
+		"/logout",
+		srv.handlers.HandleLogout(),
+	)
+	router.Get(
+		"/users/me",
+		srv.handlers.HandleUsersMe(),
+	)
 	router.Get(
 		"/messages",
 		srv.handlers.HandleGetMessages(),