dsh-shift-router: DSH's two-level model routing plugin

`dsh-shift-router` is a two-level model routing plugin for DSH, designed to intelligently allocate model usage for daily and critical cycles. It classifies requests into `fast` or `smart` tiers via an LLM Judge, adopts a strategy of "instant upgrade, trend downgrade," and pauses switching during Prompt Cache hotness to optimize costs. The plugin supports runtime failover, implementing exponential backoff cooling during service exceptions and switching only healthy models within the same tier. It also features task-level orchestration, allowing strong models to plan and delegate tasks to weak models for execution, with enforced task limits. Additionally, it provides per-tier token and cost telemetry. Installation requires Node `>=22.0.0`, and the routing mode (auto/manual/off) can be adjusted via GUI or command after configuration.