feat(api): add GET /v2/server/info endpoint for launcher compatibility

Exposes the server's configured client mode in a form that mhf-outpost
and other launcher tools can consume to warn users when their local game
version does not match what the server expects.

Returns clientMode (raw, e.g. "G9.1") and manifestId (normalized for
mhf-outpost: lowercase, dots stripped, e.g. "g91"). No auth required.

server/api/routing_test.go

@@ -44,6 +44,7 @@ func newTestRouter(s *APIServer) *mux.Router {
 	v2Auth.HandleFunc("/characters/{id}/export", s.ExportSave).Methods("GET")
 
 	v2.HandleFunc("/server/status", s.ServerStatus).Methods("GET")
+	v2.HandleFunc("/server/info", s.ServerInfo).Methods("GET")
 
 	return r
 }