feat(web): duplicates report flags identical audio under different titles (#3885)

An exact-tier group whose copies carry different titles means at least one
file's tags are wrong, and the recording the other title names may be missing
from the library. WWW (2020) was this: "WWW" was a second copy of the
instrumental, the vocal was absent, and nothing said so. The report now names
the titles and says what it implies, so the absence surfaces at the moment of
choosing which copy to keep.

Titles compare case- and whitespace-insensitively. Acoustic-tier groups are
left alone: across encodings a "Remastered" suffix is routine, not a mislabel.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/routes/admin/duplicates/duplicates.test.ts

@@ -124,6 +124,61 @@ describe('admin duplicates', () => {
     expect(text(screen.getByTestId('duplicate-tier'))).toBe('Same recording · 96% match');
   });
 
+  // #3885: identical audio titled "WWW" and "WWW (instrumental)". One file
+  // claimed to be the vocal and wasn't, and nothing said the vocal was missing.
+  describe('identical audio under different titles', () => {
+    function www() {
+      const r = response();
+      r.groups[0] = {
+        ...r.groups[0],
+        members: [member('www-01'), member('www-02', { title: 'WWW (instrumental)' })]
+      };
+      return r;
+    }
+
+    test('says the copies are titled differently and names both titles', () => {
+      renderWith(www());
+      const notice = text(screen.getByTestId('title-mismatch'));
+      expect(notice).toContain('titled “WWW” and “WWW (instrumental)”');
+      expect(notice).toContain("isn't in your library");
+    });
+
+    test('three different titles are all named', () => {
+      const r = www();
+      r.groups[0].members.push(member('www-03', { title: 'WWW (Radio Edit)' }));
+      renderWith(r);
+      expect(text(screen.getByTestId('title-mismatch'))).toContain(
+        '“WWW”, “WWW (instrumental)” and “WWW (Radio Edit)”'
+      );
+    });
+
+    test('titles differing only in case or spacing are the same title', () => {
+      const r = response();
+      r.groups[0] = {
+        ...r.groups[0],
+        members: [
+          member('www-01', { title: 'WWW (Instrumental)' }),
+          member('www-02', { title: ' www  (instrumental) ' })
+        ]
+      };
+      renderWith(r);
+      expect(screen.queryByTestId('title-mismatch')).toBeNull();
+    });
+
+    test('matching titles raise nothing', () => {
+      renderWith(response());
+      expect(screen.queryByTestId('title-mismatch')).toBeNull();
+    });
+
+    // Across encodings a "Remastered" suffix is routine, not a mislabel.
+    test('an acoustic group with different titles raises nothing', () => {
+      const r = www();
+      r.groups[0] = { ...r.groups[0], tier: 'acoustic', worst_bit_error_rate: 0.04 };
+      renderWith(r);
+      expect(screen.queryByTestId('title-mismatch')).toBeNull();
+    });
+  });
+
   // Three states all show zero groups. Each must say which it is.
   test('empty while still fingerprinting says so', () => {
     renderWith(