feat(web): Library page — owned-albums grid with cover art

New /library: GET /api/library lists LibraryItems enriched with rgMbid + year
from the matching MonitoredRelease. Client renders a cover-art grid with a live
filter; clicking an album opens the AlbumModal (tracklist). Added Library to the
nav. The album-only overview to see everything downloaded.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/app/api/library/route.test.ts

@@ -0,0 +1,29 @@
+import { describe, it, expect } from "vitest";
+import { prisma } from "@/lib/db";
+import { GET } from "./route";
+
+describe("library API", () => {
+  it("lists owned albums enriched with rgMbid + year from the matching release", async () => {
+    await prisma.monitoredRelease.create({
+      data: {
+        artistMbid: "a1", artistName: "Radiohead", rgMbid: "rg-inrainbows", album: "In Rainbows",
+        primaryType: "Album", firstReleaseDate: "2007-10-10", monitored: true, state: "fulfilled",
+      },
+    });
+    await prisma.libraryItem.create({
+      data: { artist: "Radiohead", album: "In Rainbows", path: "/m", source: "qobuz", format: "FLAC", qualityClass: 3 },
+    });
+    await prisma.libraryItem.create({
+      data: { artist: "Unknown", album: "Bootleg", path: "/m", source: "scan", format: "MP3", qualityClass: 1 },
+    });
+
+    const res = await GET();
+    expect(res.status).toBe(200);
+    const { albums } = await res.json();
+    expect(albums).toHaveLength(2);
+    const inr = albums.find((a: { album: string }) => a.album === "In Rainbows");
+    expect(inr).toMatchObject({ artist: "Radiohead", rgMbid: "rg-inrainbows", year: "2007", format: "FLAC", qualityClass: 3 });
+    const boot = albums.find((a: { album: string }) => a.album === "Bootleg");
+    expect(boot).toMatchObject({ rgMbid: null, year: null }); // no matching release → no art/tracks
+  });
+});