Web frontend: perf panel, cover warmup, incremental browse rendering

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/api/__tests__/client.test.ts

@@ -0,0 +1,20 @@
+import { describe, expect, it } from "vitest";
+
+import { coverUrl } from "../client";
+
+describe("coverUrl", () => {
+  it("is the plain full-size URL with no options", () => {
+    expect(coverUrl("abc")).toBe("/api/albums/abc/cover");
+  });
+
+  it("asks for the thumbnail and carries the cache-busting version", () => {
+    expect(coverUrl("abc", { size: "thumb", version: 42 })).toBe(
+      "/api/albums/abc/cover?size=thumb&v=42",
+    );
+  });
+
+  it("leaves the version off when there is none, so the server revalidates", () => {
+    expect(coverUrl("abc", { size: "thumb" })).toBe("/api/albums/abc/cover?size=thumb");
+    expect(coverUrl("abc", { version: 0 })).toBe("/api/albums/abc/cover");
+  });
+});