Capture screenshots

Reference live screenshots with [!snapframe]. The image right after the directive is what Neko renders — and what neko snap captures via Playwright.

[!snapframe https://example.com]
![Example homepage](/assets/example.png)

Run the capture pipeline once you've added a directive:

neko snap            # captures any missing screenshots
neko snap --all      # re-captures every screenshot, overwriting existing files

Capturing is a separate command on purpose: regular neko build stays fast and offline.