Harden release security suggestions

[debuggerone]

Summary

• harden the WebSocket wire test helper against shell execution and request-target injection
• validate Ubuntu PHP runtime installer inputs and Ondrej PPA key fingerprint
• constrain local Buildx cache paths before deleting next-cache directories
• release persistent dynamic-admin-api config strings during shutdown
• trim unnecessary Zend includes from the central King header

Checks

• php -l extension/tests/server_websocket_wire_helper.inc
• bash -n infra/scripts/install-ubuntu-php-runtime.sh infra/scripts/resolve-docker-buildx-cache.sh
• git diff --check github/main..HEAD
• local Buildx cache resolver smoke with a temp cache root