The code moves into src/: index, server and the test harness keep the root

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/panel.js

@@ -0,0 +1,18 @@
+// Live tuning panel (T key): number inputs for every TUNE value.
+
+import { TUNE } from './config.js';
+
+let panel = null;
+export function togglePanel() {
+  if (panel) { panel.remove(); panel = null; return; }
+  panel = document.createElement('div');
+  panel.style.cssText = 'position:fixed;top:8px;right:8px;background:#141a26;color:#cdd6e4;font:11px monospace;padding:8px;border:1px solid #3a4a66;max-height:90vh;overflow:auto';
+  for (const k of Object.keys(TUNE)) {
+    const row = document.createElement('div');
+    const v = TUNE[k];
+    row.innerHTML = `<label>${k} <input type="number" step="${v < 2 ? 0.02 : 1}" value="${v}" style="width:60px;background:#0c1018;color:#fff;border:1px solid #333"></label>`;
+    row.querySelector('input').oninput = e => TUNE[k] = parseFloat(e.target.value) || 0;
+    panel.appendChild(row);
+  }
+  document.body.appendChild(panel);
+}