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.

docs/CHEATSHEET.md

@@ -44,6 +44,14 @@ proxy_pool:
   refresh: 300       # re-fetch interval
   test_interval: 120 # health test cycle
   max_fails: 3       # evict after N fails
+  report_url: ""     # POST dead proxies (optional)
+```
+
+## Hot Reload
+
+```bash
+kill -HUP $(pidof s5p)                    # reload config
+podman kill --signal HUP s5p              # container reload
 ```
 
 ## Proxy File Format