docs: update project docs for SIGHUP reload and dead proxy reporting

Add hot reload section to USAGE with reloadable settings table.
Add dead proxy reporting section with report_url config and payload
format. Update example.yaml, ROADMAP, TASKS, TODO, CHEATSHEET.

TODO.md

@@ -5,9 +5,7 @@
 - SOCKS5 BIND and UDP ASSOCIATE commands
 - Chain randomization modes (round-robin, sticky-per-destination)
 - Per-destination chain rules (bypass chain for local addresses)
-- Hot config reload on SIGHUP
 - Systemd socket activation
-- Report dead proxies back to source API
 
 ## Performance