Repair Linux full-V8 CSS custom-property compilation #822

Problem

Current main native-package run 35507911399 fails the Linux full-V8 build in webscene_v8_runtime.cpp and webscene_v8_runtime_css_parsing.inc.

The typed registered-custom-property animation work introduced CSS runtime types in conditional native build paths without completing the required qualification/aliasing:

• implementation::registered_custom_property has no alias in webscene_v8_runtime_state_types.inc, so the state member is not declared in this profile.
• read_memory_metrics() is outside implementation but refers to css_opacity_keyframes without qualification.
• register_custom_property(registered_custom_property) is parsed as the member function name instead of the CSS type in this scope.

The portable managed build did not compile this exact full-V8/CSS parser combination, so the defect reached main.

Proposed fix

• Add the missing implementation alias for webscene_native::css::registered_custom_property.
• Qualify nested keyframe stop types from the implementation scope.
• Qualify the parser callback parameter as css::registered_custom_property.
• Add a source-level compile contract for these conditional references so the same regression fails before the expensive package build.

Acceptance

• The focused source/compile contract passes.
• Linux full-V8 Runtime package compilation passes the affected translation unit.
• Current-main native package CI no longer fails on these symbols.

Evidence

• Failing run: https://github.com/SceneTech/WebScene/actions/runs/35507911399
• Parent program: [Epic] Complete remaining Code OSS native release acceptance #227