nx_browser_render_shot.nx

nx_browser_render_shot.nx -- R2 proof probe for the CSS-on-native-Windows arc. Reads an HTML file, runs the EXTRACTED render organ (br_layout -> CSS cascade + box layout; br_shot_png -> RGBA framebuffer paint -> PNG), prints box-count + page_h. Verifies nx_browser_render.nx is correct (WSL run) and, built through a keystone, that the CSS layout+paint runs as a native Windows PE. NOT shipped -- a render gate.