feat: detect & link album mentions, not just artists (closes task/album-detection)

Source: task/album-detection (objective/linker-improvements) — project brief asks for artist OR album linking; MVP linked artists only.

- service/lib.js: pickAlbum (the exact-name gate, named for the album path) + linkResult now carries kind:"artist"|"album" (additive; defaults to artist so older clients keep working).
- service/resolver.js: one Spotify type=artist,album search per candidate, exact-match against either; returns {url,kind}; cache key includes the kind hint. resolveOne/resolveAll thread the LLM kind hint through.
- service/llm.js: parseClassification now returns Map(name -> "artist"|"album") so album-kind candidates route to the album path (.has() still works like the old Set).
- extension/extract.js: albumMatchesIn over two precise signals (quoted strings + album cue phrases "the album X", "X LP/EP"), folded into allMatchesIn.
- extension/content.js + styles.css: album links render italicised (.rsl-album) with an album tooltip; artist behavior unchanged.
- Tests: new pure-logic coverage in lib.test.js / llm.test.js / extract.test.cjs (album shaping, Map-kind routing, album candidate extraction). scripts/check.sh green.
- README.md + AGENTS.md: document album linking.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

service/llm.test.js

@@ -31,12 +31,28 @@ test("parseClassification keeps only artist/album candidates that were in the li
   assert.ok(!got.has("the best part"));
 });
 
+test("parseClassification returns a Map of norm(name) -> kind for routing", () => {
+  const got = parseClassification(
+    JSON.stringify({
+      results: [
+        { name: "Cattle Decapitation", kind: "artist" },
+        { name: "Reek of Putrefaction", kind: "ALBUM" }, // case-insensitive kind
+      ],
+    }),
+    ["Cattle Decapitation", "Reek of Putrefaction"],
+  );
+  assert.ok(got instanceof Map);
+  assert.equal(got.get("cattle decapitation"), "artist");
+  assert.equal(got.get("reek of putrefaction"), "album"); // normalized to lowercase kind
+});
+
 test("parseClassification accepts album kind and a bare array reply", () => {
   const got = parseClassification(
     JSON.stringify([{ name: "Reek of Putrefaction", kind: "album" }]),
     ["Reek of Putrefaction"],
   );
   assert.ok(got.has("reek of putrefaction"));
+  assert.equal(got.get("reek of putrefaction"), "album");
 });
 
 test("parseClassification ignores hallucinated names not in the candidate list", () => {