End-to-end rasterization behind the render feature (which now enables
obscura-render/paint):
- obscura-render: screenshot_png(dom, viewport) paints and encodes to PNG
via tiny-skia's encode_png (no extra dep).
- obscura-browser: Page::screenshot renders the live DOM at a viewport.
- CLI: obscura fetch --screenshot out.png writes the settled page to a PNG.
- CDP: Page.captureScreenshot returns the PNG base64-encoded, so
Puppeteer/Playwright page.screenshot() works. captureSnapshot still
errors (it is a DOM/layer snapshot, not an image).
Verified: both paths produce correct 1280x720 RGBA PNGs with elements
laid out and colored as the CSS specifies (block stacking, backgrounds,
white page). Default build unchanged; obstacle course 33/33.
Text, borders, and images are not yet painted; the box layout and
background colors are rendered.
Adds a paint feature to obscura-render (tiny-skia: pure Rust, CPU,
deterministic, no system deps). paint_dom lays out the DOM and fills
each element's border box with its parsed background-color over a white
page, in tree order so descendants paint over ancestors.
Style parsing now also extracts background-color (hex #rgb/#rgba/
later enhancements.
SGavrl