tools: add router cluster benchmark controller workflow

## Problem

There is no repository-guided workflow for running repeatable sysbench benchmarks against a router/TiDB cluster over SSH. Operators currently need to piece together remote environment preparation, TiUP bootstrap, topology selection, and sequential thread-based benchmark rounds manually.

## Proposal

Add a reusable skill plus helper scripts that:
- prepare a remote router-cluster benchmark environment
- use the repository's router topology template to resolve TiDB endpoints
- run deterministic single-round or multi-round sysbench controller benchmarks with wait gates between rounds

## Expected benefit

This makes router-cluster benchmarking repeatable, reduces operator error, and documents the controller-style execution contract in-repo.