The deploy gate only installs chromium, so imaging had no browser-level
coverage. Add two Playwright specs:
- e2e/imaging/avatar-endpoint.spec.ts: HTTP contract for the avatar
(/api/imaging/avatar), default (/imaging) and badge endpoints — animated
APNG for a figure with an effect, the trailing-`.0` regression figure,
ETag/304 revalidation, and a 400 for a malformed figure. Runs in the
deploy gate automatically via the default Playwright config.
- e2e/imaging/avatar-render.spec.ts: loads the avatar in a real browser and
asserts it decodes at a non-zero size and animates. Navigates to the image
URL directly so production CSP `upgrade-insecure-requests` cannot rewrite
the request over a plain-HTTP host.
Add playwright.imaging.config.ts running both across chromium, firefox and
webkit, a `test:imaging` script, and a non-blocking CI job that installs all
three engines and checks the live site.
