Preserve configured public origin for proxy

[chen21019]

Result

• preserve only the reviewed PROXY_PLATFORM_PUBLIC_ORIGIN value when the Engine rebuilds the WebSocket Proxy child environment
• continue clearing unrelated inherited and unreviewed PROXY_* variables
• publish numeric Engine version 0.183.295 and align release metadata

Validation

• 48-module Maven reactor: passed
• WebsocketProxyLauncherSettingsTest: 10/10 passed
• scripts/check-pasturestack-source: passed
• git diff --check: passed
• Codex Security diff scan: complete coverage, 0 findings