Two changes requested by the user:
1. Fold the hand-holding quickstart tutorial into README §3 (both
languages). Delete docs/quickstart.md and docs/quickstart.zh-CN.md.
Remove them from all 5 validator DOCS lists, README §6 doc index,
and charter §7 boundary table. The tutorial now lives as
README §3.0–§3.11: prerequisites, create Telegram bot, find chat id,
get JMAP credentials, run backend, sign in, fill config, register
callbacks, enable processing, verify, schedule drain, troubleshoot.
2. Replace 'gateway'/'网关' with 'load balancer'/'负载均衡器' across
all markdown (README, docs/, AGENTS.md, cloudflare-worker/README).
Also fix 4 markdown anchor links whose heading slugs changed.
Also fix charter §8 '18 safe routes' → '19' (was missed in the
earlier reference.md fix).
GATE-DOCS 6/6 PASS (71 anchors, 727 path-refs, 455 sec-refs).