Meter: proper clipping indicators

- Dedicated clip LED at the hot end (default on): lights when the
  signal reaches clipThreshold (default max), holds for clipHold ms or
  latches until clicked ('latch'); clipColor, onClip callback,
  data-clipped root attribute, data-part=clip for CSS
- clipValue prop: separate signal for clip detection so the bar can
  show RMS while the LED watches sample peaks, like real meters
- Synth: analyser loop now computes sample peaks alongside RMS and
  feeds them to the clip detector - overdriving the synth genuinely
  trips the LED
- Gallery meter demo throws occasional hot transients to exercise it;
  API docs and README updated

apps/docs/src/sections/Gallery.tsx

@@ -108,9 +108,11 @@ const MeterDemo: React.FC = () => {
     let t = 0;
     const id = setInterval(() => {
       t += 0.09;
+      // Occasional hot transient so the clip LED gets to do its job.
+      const spike = Math.random() < 0.04 ? 9 : 0;
       setLevels([
-        -13 + Math.sin(t) * 6 + Math.random() * 7,
-        -14 + Math.sin(t * 1.3 + 1) * 6 + Math.random() * 7,
+        -13 + Math.sin(t) * 6 + Math.random() * 7 + spike,
+        -14 + Math.sin(t * 1.3 + 1) * 6 + Math.random() * 7 + spike,
       ]);
     }, 90);
     return () => clearInterval(id);
@@ -341,7 +343,7 @@ export const Gallery: React.FC = () => (
           </div>
         </Card>
 
-        <Card title="Meter" desc="Read-only LED metering with peak hold — the display sibling of LEDFader." tag="<Meter peakHold={1200} />">
+        <Card title="Meter" desc="Read-only LED metering with peak hold and a latching clip LED — click it to clear." tag="<Meter clipHold={1500} />">
           <MeterDemo />
         </Card>