Auto VJ: a director that adapts the visuals to the playing track in real time

The audio engine now tracks musical features: fast/slow energy EMAs, BPM
(median of beat intervals), a quiet/groove/peak mood with hysteresis, and
drop detection (fast energy diverging from slow right after a lull). An
output-side director, toggled from the control UI, switches presets every
16 beats (or ~14s without beats) and immediately on a drop, drawing from
mood-matched family pools (scenic for quiet, fluid/geometry for groove,
fractals/tunnels/fire for peak) while avoiding recent repeats. A manual
effect pick takes over and turns the director off.

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

src/control.html

@@ -108,6 +108,7 @@
       <section class="span2" id="effects-section">
         <label>Libreria effetti <span id="effects-count"></span></label>
         <div class="row">
+          <button id="auto-vj" title="L'Auto VJ ascolta il brano (energia, BPM, drop) e cambia effetto da solo a tempo di musica">🤖 Auto VJ</button>
           <select id="effect-family"><option value="-1">Tutte le famiglie</option></select>
           <input type="text" id="effect-search" class="textfield" placeholder="Cerca effetto…" />
         </div>