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/data/modelEligibility.test.mjs

@@ -0,0 +1,48 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import { selectModelEligible } from './modelEligibility.js';
+
+const ADD_SQ = 100 * 100;
+
+test('visible contacts win the cap before off-screen retained models', () => {
+  // Nearest first: an off-screen retained model, then two on-screen contacts.
+  const candidates = [
+    ['off-kept', 10, false],
+    ['on-new', 20, true],
+    ['on-kept', 30, true],
+  ];
+  const modeled = new Set(['off-kept', 'on-kept']);
+  const eligible = selectModelEligible(candidates, {
+    cap: 2,
+    addDistSq: ADD_SQ,
+    isModeled: (id) => modeled.has(id),
+  });
+  assert.deepEqual([...eligible], ['on-kept', 'on-new']);
+});
+
+test('retained models keep their slot beyond the add radius; new ones do not', () => {
+  const candidates = [
+    ['near-new', 50, true],
+    ['far-kept', ADD_SQ + 1, true],
+    ['far-new', ADD_SQ + 2, true],
+    ['off-new', 60, false],
+  ];
+  const eligible = selectModelEligible(candidates, {
+    cap: 10,
+    addDistSq: ADD_SQ,
+    isModeled: (id) => id === 'far-kept',
+  });
+  assert.deepEqual([...eligible], ['far-kept', 'near-new', 'off-new']);
+});
+
+test('an empty cap admits nothing', () => {
+  assert.equal(
+    selectModelEligible([['a', 1, true]], {
+      cap: 0,
+      addDistSq: ADD_SQ,
+      isModeled: () => true,
+    }).size,
+    0,
+  );
+});