docs: add proxy-neutral Apache reverse proxy setup

[bifrost0x]

Summary

• document the proxy-neutral forwarding contract used by WebSSH
• add Apache httpd 2.4.47+ examples for root and subfolder deployments
• align the Nginx examples with the documented X-Forwarded-Host contract
• document trusted proxy counts, secure origins, cookies, and private backend networking

Validation

• npm run test:js (229 passed)
• README consistency checks
• git diff --check

Local limitations

• Python tests were not run because the local Python runtimes do not include the WebSSH test dependencies
• apachectl -t was not available because Apache and the Docker daemon are not running locally; directives were checked against the official Apache HTTP Server 2.4 documentation

Related discussion: #121

[chatgpt-codex-connector]

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