@visol-456/dsh-llm-fallback: Provider Fallback Chain Plugin for DSH

`@visol-456/dsh-llm-fallback` is a community plugin for DeepSeek Harness, designed to address the issue where single-provider deployments fail directly when requests encounter rate limiting, timeouts, or exceptions. This plugin allows automatic failover to a backup `(provider, model)` target for retrying the same request based on configured priority when the primary provider fails. Core features include maintaining a backup list, triggering failover based on failure codes, a circuit breaker mechanism, and configuration management through a Web UI. Configuration supports hot updates without requiring a service restart, and persistent session events are logged for auditing purposes. Installation can be done via `dsh plugin add` or npm, with mounting and configuration of `fallba` required in `cordis.yml`.