fix(plugin): support public IP override behind NAT

[rumblefrog]

Summary

• add a validated ServerIP override for servers whose hostip resolves to a private container or LAN address
• apply the resolved address consistently to core bans, SourceComms, admin loading, queued writes, and auto-registration
• make reloads refresh server identity safely and snapshot auto-registration context across asynchronous callbacks
• document the NAT setup in the shipped config and operator guides

Testing

• SourcePawn 1.12.0.7253: resolve plugin version and compile every top-level plugin
• cd docs && npm run build
• adversarial review completed with no remaining findings

Closes #1555