feat(library): genre sliders, artist links, and navigation utils

- music landing: diverse per-genre album sliders (online counts /
  offline wide-probe fallback) and home-screen library shortcuts
- add ArtistLinks component and shared navigation/genreDiversity utils
- player/playback-mode refinements across Rust and frontend

src/lib/components/library/ArtistLinks.test.ts

@@ -0,0 +1,57 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { render, screen, fireEvent } from "@testing-library/svelte";
+import ArtistLinks from "./ArtistLinks.svelte";
+
+const goto = vi.fn();
+vi.mock("$app/navigation", () => ({
+  goto: (...args: unknown[]) => goto(...args),
+}));
+
+describe("ArtistLinks", () => {
+  beforeEach(() => goto.mockClear());
+
+  it("renders a clickable link per artist that navigates to its detail page", async () => {
+    render(ArtistLinks, {
+      artistItems: [
+        { id: "a1", name: "Radiohead" },
+        { id: "a2", name: "Thom Yorke" },
+      ],
+    });
+
+    const link = screen.getByRole("button", { name: "Radiohead" });
+    await fireEvent.click(link);
+
+    expect(goto).toHaveBeenCalledWith("/library/a1");
+    expect(screen.getByRole("button", { name: "Thom Yorke" })).toBeTruthy();
+  });
+
+  it("falls back to plain text when only names (no ids) are available", () => {
+    render(ArtistLinks, { artists: ["Unknown Artist"] });
+
+    expect(screen.queryByRole("button")).toBeNull();
+    expect(screen.getByText("Unknown Artist")).toBeTruthy();
+  });
+
+  it("ignores artistItems with blank ids and uses the names fallback", () => {
+    render(ArtistLinks, {
+      artistItems: [{ id: "  ", name: "No Id Artist" }],
+      artists: ["No Id Artist"],
+    });
+
+    expect(screen.queryByRole("button")).toBeNull();
+    expect(screen.getByText("No Id Artist")).toBeTruthy();
+  });
+
+  it("calls onNavigate before navigating (e.g. to close a player)", async () => {
+    const onNavigate = vi.fn();
+    render(ArtistLinks, {
+      artistItems: [{ id: "a1", name: "Radiohead" }],
+      onNavigate,
+    });
+
+    await fireEvent.click(screen.getByRole("button", { name: "Radiohead" }));
+
+    expect(onNavigate).toHaveBeenCalledOnce();
+    expect(goto).toHaveBeenCalledWith("/library/a1");
+  });
+});