docs: update AGENTS.md and README for new features, add JS tests

Docs:
- AGENTS.md: updated toolchain section with js-lint/js-test tasks,
  expanded web/ui/ directory listing, added event delegation and
  Web Audio API to key patterns, updated testing section
- README: marked issue #9 (Audio Preview Player) as done
- .gitignore: added akai-fetch.test and cover.out

Tests:
- Moved groupWavs and cleanName to util.js (pure functions)
- Added 10 new JS tests: 6 groupWavs, 4 cleanName
- Total JS tests: 29 (up from 19)

web/ui/app.js

@@ -200,29 +200,6 @@ let animationFrame = null;
 
 document.getElementById('wav-browse-btn').addEventListener('click', browseWavs);
 
-function groupWavs(paths) {
-  const libs = {};
-  for (const p of paths) {
-    const parts = p.split('/');
-    let lib, prog, file;
-    if (parts.length === 1) {
-      file = parts[0];
-    } else if (parts.length === 2) {
-      lib = parts[0]; prog = parts[0]; file = parts[1];
-    } else {
-      lib = parts[0]; prog = parts[1]; file = parts[parts.length - 1];
-    }
-    if (!libs[lib]) libs[lib] = {};
-    if (!libs[lib][prog]) libs[lib][prog] = [];
-    libs[lib][prog].push({ fullPath: p, name: file.replace(/\.wav$/i, '') });
-  }
-  return libs;
-}
-
-function cleanName(name) {
-  return name.replace(/_+/g, ' ').trim();
-}
-
 function renderSampleCards(samples) {
   return samples.map(s => `
     <div class="sample-card" data-action="play" data-wav="${esc(s.fullPath)}">