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/style.css

@@ -796,3 +796,6 @@ kbd {
   padding: 1px 5px;
   margin: 0 1px;
 }
+
+/* Auto VJ toggle */
+#auto-vj.vj-on { background: #2e7d32; border-color: #4caf50; color: #fff; }