feat: room-based calls + AudioWorklet for capture and playback

Rooms:
- URL-based: open /myroom to join a room
- Two clients in same room get bridged through relay
- Input field for room name, also supports URL path and hash
- Each room creates independent relay connections

AudioWorklet (replaces deprecated ScriptProcessorNode):
- capture-processor.js: accumulates mic samples, sends 960-sample frames
- playback-processor.js: pull-based output with 200ms buffer cap
- Falls back to ScriptProcessor if AudioWorklet unavailable
- Eliminates drift: worklet runs on audio thread, not main thread

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/wzp-web/static/audio-processor.js

@@ -0,0 +1,39 @@
+// AudioWorklet processor for capturing microphone audio.
+// Accumulates samples and posts 960-sample (20ms @ 48kHz) frames to the main thread.
+
+class CaptureProcessor extends AudioWorkletProcessor {
+  constructor() {
+    super();
+    this.buffer = new Float32Array(0);
+  }
+
+  process(inputs, outputs, parameters) {
+    const input = inputs[0];
+    if (!input || !input[0]) return true;
+
+    const samples = input[0]; // Float32Array, typically 128 samples
+
+    // Accumulate
+    const newBuf = new Float32Array(this.buffer.length + samples.length);
+    newBuf.set(this.buffer);
+    newBuf.set(samples, this.buffer.length);
+    this.buffer = newBuf;
+
+    // Send complete 960-sample frames
+    while (this.buffer.length >= 960) {
+      const frame = this.buffer.slice(0, 960);
+      this.buffer = this.buffer.slice(960);
+
+      // Convert to Int16
+      const pcm = new Int16Array(960);
+      for (let i = 0; i < 960; i++) {
+        pcm[i] = Math.max(-32768, Math.min(32767, Math.round(frame[i] * 32767)));
+      }
+      this.port.postMessage(pcm.buffer, [pcm.buffer]);
+    }
+
+    return true;
+  }
+}
+
+registerProcessor('capture-processor', CaptureProcessor);