Chain driver

Single-session driver for a multi-iteration skill-chain run. Invokes `bin/skill-chain.py --chain <name> --loop N` with budget gates and Telegram event notifications as native flags. Posts Telegram updates at session start, each iteration boundary (commit + per-iter spend + cumulative), every rate-limit pause/resume, supervisor escalation, and session end. Honors a `--max-budget-usd` halt and a `--max-cycles` halt independently of the chain's own loop count. Distinct from sst-manager (cron-based, multi-project, periodic) and from sst-skill-router (in-process planner inside one user request). The proprietary counterpart supplies the watched-chain name, Telegram chat ID, and…