dsh-system-proxy: DSH Outbound HTTP(S) Routing Plugin

dsh-system-proxy is a DSH host plugin designed to uniformly handle outbound HTTP/HTTPS request routing, avoiding duplicate proxy logic across plugins. This plugin supports multiple proxy protocols and multiple named proxies, providing fine-grained routing rules based on host, provider, or plugin, with four actions: direct connection, forced proxy, failover fallback, and blocking. Its core features include a secure fallback mechanism (only allowing idempotent requests to be automatically replayed), direct connection protection for intranet and cloud metadata endpoints, secure storage of proxy credentials (submitted via `passwordRef` and cleared from drafts), and global `fetch` and Node.js HTTP module patch support. Running requires Node.js >=22. Callers are identified through explicit context identifiers to ensure clear route ownership, while interactive configuration cards and environment variables are also provided.