[grobf5]

Summary

This PR bundles recent core hardening and full documentation synchronization:

• Interruption & Signal Safety: Traps SIGINT (Ctrl+C) and SIGTERM globally, cleans up in-flight partial downloads (.part files), cleanly releases active SSH/SCP sessions, and gracefully drains HTTP connections without leaving corrupted disk files or lingering network handles.
• Documentation Synchronization: Comprehensive updates across README.md, docs/cli.md, docs/network_and_firewall.md, docs/appliance_push.md, and docs/downloads.md covering Outbound Proxy (HTTP CONNECT & SOCKS5), Case Creation Wizard, GeoIP automation, bigip info/serial, and current API state (including live 500 defect on /cases/metadata).
• BIG-IP Appliance Shell Hardening: Detects and accommodates appliances where the administrative SSH user has tmsh configured as the default login shell, automatically falling back to direct tmsh command syntax for bigip info and bigip serial.
• AWS Testenv Gitignoring & Watchdog: Gitignores the testenv/ automated testing suite with 4-hour automatic power-off watchdogs.

Testing

• make all (fmt, vet, unit tests with race detector, build): 100% PASS.
• Live verification against AWS test lab with and without proxy (HTTP & SOCKS5).
• Live verification against TMOS 17.5.1.9 BYOL VE node.