Security: validate nested stream wrapper in stream: resource (CWE-22) (#1195)
The built-in stream: resource type let a template bypass Security stream
restrictions. BasePlugin::load() matches the 'stream' sysplugin before the
stream_get_wrappers()/isTrustedStream() check, so a resource such as
stream:php://filter/read=convert.base64-encode/resource=/path was opened by
StreamPlugin::getContent() via fopen() on the nested php:// wrapper without
ever validating it. This bypassed Security::$streams (including
Security::$streams = null) and allowed reading arbitrary local files.
Parse the wrapper scheme from the resolved path in StreamPlugin::getContent()
and validate it with Security::isTrustedStream() before fopen(), giving the
stream: resource the same check the direct wrapper path already receives.
Adds regression tests covering the disabled-streams bypass, the
not-on-allowlist case, and a positive test that an explicitly allowed wrapper
still works.