test(imaging): add endpoint contract e2e and cross-browser render checks

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.

e2e/imaging/avatar-endpoint.spec.ts

@@ -0,0 +1,91 @@
+import { expect, test } from "@playwright/test";
+
+// The exact figure that regressed in production: the game client appends a
+// trailing `.<n>` segment that the renderer ignores, but the previous
+// validation regex rejected with a 400.
+const FIGURE =
+	"hr-11782-40-40.hd-180-7-14.ch-11592-66.lg-10726-79-1408.sh-11764-1408.ha-11958-70-1408.wa-2007-0.0";
+
+const avatarPath = (params: Record<string, string> = {}) =>
+	`/api/imaging/avatar?${new URLSearchParams({ figure: FIGURE, ...params })}`;
+
+function countBytes(haystack: Buffer, needle: Buffer): number {
+	let count = 0;
+	for (
+		let index = haystack.indexOf(needle);
+		index !== -1;
+		index = haystack.indexOf(needle, index + needle.length)
+	) {
+		count += 1;
+	}
+	return count;
+}
+
+test("renders an animated APNG for a figure with an effect", async ({
+	request,
+}) => {
+	const response = await request.get(
+		avatarPath({ img_format: "apng", effect: "14" }),
+	);
+	expect(response.status()).toBe(200);
+	expect(response.headers()["content-type"]).toContain("image/");
+	// `unavailable` means the placeholder was served, i.e. no real render.
+	expect(response.headers()["x-imager-source"]).not.toBe("unavailable");
+
+	const body = await response.body();
+	expect(body.length).toBeGreaterThan(1000);
+	// APNG signature chunks: `acTL` announces the animation, `fcTL` marks frames.
+	expect(body.includes(Buffer.from("acTL"))).toBe(true);
+	expect(countBytes(body, Buffer.from("fcTL"))).toBeGreaterThan(1);
+});
+
+test("serves a static PNG when no animation is requested", async ({
+	request,
+}) => {
+	const response = await request.get(avatarPath({ img_format: "png" }));
+	expect(response.status()).toBe(200);
+	expect(response.headers()["content-type"]).toContain("image/png");
+	const body = await response.body();
+	expect(body.subarray(1, 4).toString("ascii")).toBe("PNG");
+});
+
+test("answers conditional requests with 304", async ({ request }) => {
+	const first = await request.get(avatarPath({ img_format: "png" }));
+	expect(first.status()).toBe(200);
+	const etag = first.headers()["etag"];
+	expect(etag).toBeTruthy();
+
+	const second = await request.get(avatarPath({ img_format: "png" }), {
+		headers: { "if-none-match": etag as string },
+	});
+	expect(second.status()).toBe(304);
+	expect(second.headers()["etag"]).toBe(etag);
+});
+
+test("rejects a malformed figure with 400", async ({ request }) => {
+	const response = await request.get(avatarPath({ figure: "../bad" }));
+	expect(response.status()).toBe(400);
+});
+
+test("the default /imaging endpoint serves a PNG", async ({ request }) => {
+	const response = await request.get(
+		`/imaging?${new URLSearchParams({ figure: FIGURE, img_format: "png" })}`,
+	);
+	expect(response.status()).toBe(200);
+	expect(response.headers()["content-type"]).toContain("image/png");
+});
+
+test("the badge endpoint serves an image and revalidates", async ({
+	request,
+}) => {
+	const first = await request.get("/api/imaging/badge?code=ADM");
+	expect(first.status()).toBe(200);
+	expect(first.headers()["content-type"]).toContain("image/");
+	const etag = first.headers()["etag"];
+	expect(etag).toBeTruthy();
+
+	const second = await request.get("/api/imaging/badge?code=ADM", {
+		headers: { "if-none-match": etag as string },
+	});
+	expect(second.status()).toBe(304);
+});