feat(sdr): local receivers — browser RTL-SDR, Local ADS-B layer and decoder feeds (#732)

Adds a Local ADS-B layer fed by your own receivers: a browser WebUSB
RTL-SDR (with FM listening) and local 1090/978 MHz decoder feeds
(LOCAL_RECEIVER_FEEDS, local and private addresses only). Local aircraft
draw in magenta with class, silhouettes, 3D models, trails and a position
sanity filter; the click card names the band and input that heard them.

Builds on Sameh Khamis's SDR prototype and the initial GEV port by
Mazeyar Moeini Feizabadi (#134); the decoder-feed design follows the
notes on #57. Closes #57.

Co-authored-by: Sameh Khamis <[email protected]>
Co-authored-by: Mazeyar Moeini Feizabadi <[email protected]>

src/sdr/sdrAudioWorklet.js

@@ -0,0 +1,48 @@
+class GevSdrAudioPlayer extends AudioWorkletProcessor {
+  constructor() {
+    super();
+    this.queue = [];
+    this.offset = 0;
+    this.volume = 0.8;
+    this.port.onmessage = (event) => {
+      if (
+        event.data?.type === 'samples' &&
+        event.data.samples instanceof Float32Array
+      ) {
+        this.queue.push(event.data.samples);
+        if (this.queue.length > 48)
+          this.queue.splice(0, this.queue.length - 48);
+      } else if (event.data?.type === 'volume') {
+        this.volume = Math.max(0, Math.min(1, Number(event.data.value) || 0));
+      } else if (event.data?.type === 'clear') {
+        this.queue.length = 0;
+        this.offset = 0;
+      }
+    };
+  }
+
+  process(_inputs, outputs) {
+    const output = outputs[0]?.[0];
+    if (!output) return true;
+    output.fill(0);
+    let outputOffset = 0;
+    while (outputOffset < output.length && this.queue.length) {
+      const samples = this.queue[0];
+      const available = samples.length - this.offset;
+      const count = Math.min(output.length - outputOffset, available);
+      for (let index = 0; index < count; index += 1) {
+        output[outputOffset + index] =
+          samples[this.offset + index] * this.volume;
+      }
+      outputOffset += count;
+      this.offset += count;
+      if (this.offset >= samples.length) {
+        this.queue.shift();
+        this.offset = 0;
+      }
+    }
+    return true;
+  }
+}
+
+registerProcessor('gev-sdr-audio-player', GevSdrAudioPlayer);