Split app.js into one script per feature; versioning covers every public file; README for the new features

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

tools/lyrics-test.js

@@ -18,7 +18,7 @@ const lrcLib = require('../lyrics');
   ok('word timing inside a line is read', l[1].words && l[1].words.length === 2 && l[1].words[0].t === 14000 && l[1].words[1].t === 14800 && l[1].text === 'Second line', l[1]);
   ok('a line that repeats (two times) appears twice, in order', l[2].text === 'Chorus' && l[3].text === 'Chorus' && l[3].t === 30250, l.slice(2));
   const client = (() => { // the same reader in the app itself must agree
-    const src = fs.readFileSync(path.join(root, 'public', 'app.js'), 'utf8'), a = src.indexOf('function lyrParseLrc'), b = src.indexOf('\n}\n', a) + 3;
+    const src = fs.readFileSync(path.join(root, 'public', 'lyrics-view.js'), 'utf8'), a = src.indexOf('function lyrParseLrc'), b = src.indexOf('\n}\n', a) + 3;
     return new Function(src.slice(a, b) + '; return lyrParseLrc;')();
   })();
   ok('and the app reads it the same way', JSON.stringify(client('[ti:x]\n[00:10.50]Hello there\n[00:14.00]<00:14.00>Second <00:14.80>line\n[00:20.00][00:30.25]Chorus\n')) === JSON.stringify(l));