Merge upstream/main: air-quality layer (AQHI) meets i18n

Upstream's #568 adds the Air quality layer to the Weather group (ECCC
AQHI, Canada only) with a band legend, worst-first list and voice
support.

- package-boundaries: both sides' entries unioned.
- layerPanel/weatherPanel tests: both sides' new tests kept; the
  weatherPanel fixture follows upstream (legendCategorical: true, the
  'list' block id) while our localized-history (K-6) test stays.
- air-quality strings marked: band labels and the provider label as
  msg() data, the readings-list aria-label through t(); es/ru entries
  added (+6 keys each).
- The synthetic air-quality allocation-benchmark titles follow the
  file's own convention (// i18n-ignore) like TRK/VESSEL/CAMERA.

Also verified the auto-merged weatherPanel.js against upstream: ORDER
gains 'air-quality', OBSERVED stays slice(2, 5), and the data-driven
legendCategorical path is upstream's.

npm run i18n: complete (2559), no unmarked strings. npm test: only the
pre-existing environmental OPENAI_API_KEY leak fails. Build passes.

src/overlays/worldOverlayAllocation.worker.mjs

@@ -26,6 +26,12 @@ import {
   TRACKED_OVERLAY_SOURCE_OPTIONS,
 } from '../data/trackedReadout.js';
 import { CCTV_AMBIENT_CARD_MAX } from '../data/cctvLod.js';
+import {
+  AIR_QUALITY_OVERLAY_COHORT_LIMIT,
+  AIR_QUALITY_OVERLAY_COLLISION_CAPACITY,
+  AIR_QUALITY_OVERLAY_SOURCE_ID,
+  createAirQualityOverlayEntry,
+} from '../layers/airQuality/model.js';
 import {
   CCTV_OVERLAY_SOURCE_ID,
   createCctvThumbnailOverlayEntry,
@@ -1110,6 +1116,69 @@ function buildSubmarineCablesWorkload(count) {
   );
 }
 
+/**
+ * The air-quality station cohort at full size.
+ *
+ * Measured standalone (the submarine-cable precedent) rather than stacked on
+ * the Phase-5 host: air-quality stations are sparse and, with the single
+ * currently-registered provider, continental — so the question a budget has to
+ * answer is what its own cohort costs, not what it adds to a worldwide worst
+ * case it never shares a viewport with. The entry shape is the same static
+ * `ambient-label` the earthquake layer publishes, so the per-candidate ceiling
+ * is the meaningful gate.
+ */
+function buildAirQualityWorkload(count) {
+  if (count !== AIR_QUALITY_OVERLAY_COHORT_LIMIT) {
+    throw new Error(
+      `air-quality requires ${AIR_QUALITY_OVERLAY_COHORT_LIMIT} entries`,
+    );
+  }
+  const workload = {
+    entries: [],
+    positions: [],
+    drifts: [],
+    registrations: [],
+  };
+  const columns = Math.max(1, Math.ceil(Math.sqrt((count * 16) / 9)));
+  const rows = Math.max(1, Math.ceil(count / columns));
+  const spanX = columns > 1 ? 1.68 / (columns - 1) : 0;
+  const spanY = rows > 1 ? 1.56 / (rows - 1) : 0;
+  const stations = [];
+  for (let index = 0; index < count; index++) {
+    const column = index % columns;
+    const row = Math.floor(index / columns);
+    const baseX = -0.84 + column * spanX;
+    const baseY = -0.78 + row * spanY;
+    const position = new Cesium.Cartesian3(baseX, baseY, 0);
+    workload.positions.push(position);
+    workload.drifts.push({
+      baseX,
+      baseY,
+      phase: index * 0.27,
+      rate: 0.32 + (index % 6) * 0.04,
+    });
+    const entry = createAirQualityOverlayEntry({
+      id: `air-${index}`,
+      position,
+      // i18n-ignore: synthetic allocation-benchmark fixture, not shown as UI
+      title: `Station ${index} ${1 + (index % 10)}`,
+      accent: '#4cc9f0',
+      value: 1 + (index % 10),
+    });
+    entry.horizonCull = false;
+    stations.push(entry);
+  }
+  workload.registrations.push({
+    sourceId: AIR_QUALITY_OVERLAY_SOURCE_ID,
+    entries: stations,
+    options: {
+      cohortLimit: AIR_QUALITY_OVERLAY_COHORT_LIMIT,
+      collisionCapacity: AIR_QUALITY_OVERLAY_COLLISION_CAPACITY,
+    },
+  });
+  return workload;
+}
+
 function buildPhase6DetectionWorkload(count) {
   const random = makeRandom(0xd37ec710);
   const positions = [];
@@ -1215,9 +1284,13 @@ function main() {
                                 ? buildPhase5RocketMissionWorkload(ENTRY_COUNT)
                                 : PROFILE === 'all-live-radio'
                                   ? buildAllLiveRadioWorkload(ENTRY_COUNT)
-                                  : PROFILE === 'submarine-cables'
-                                    ? buildSubmarineCablesWorkload(ENTRY_COUNT)
-                                    : buildWorkload(ENTRY_COUNT);
+                                  : PROFILE === 'air-quality'
+                                    ? buildAirQualityWorkload(ENTRY_COUNT)
+                                    : PROFILE === 'submarine-cables'
+                                      ? buildSubmarineCablesWorkload(
+                                          ENTRY_COUNT,
+                                        )
+                                      : buildWorkload(ENTRY_COUNT);
   const { entries, positions, drifts } = workload;
   const solveIntervalMs = Number(process.env.GEV_ALLOC_SOLVE_MS) || 125;
   const detectionActive = !!workload.detectionLayer;