docs: update project docs for warm start and chain health check

Add warm start and chain pre-flight sections to USAGE. Mark both
features complete in ROADMAP and TASKS. Remove implemented items
from TODO. Update README, PROJECT, and CHEATSHEET.

TODO.md

@@ -7,9 +7,7 @@
 - Per-destination chain rules (bypass chain for local addresses)
 - Hot config reload on SIGHUP
 - Systemd socket activation
-- Parallel health tests at startup (fast warm start)
 - Report dead proxies back to source API
-- Chain health check (test static chain before pool tests)
 
 ## Performance