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.

CHANGELOG.md

@@ -191,6 +191,19 @@
 
 ## [Unreleased]
 
+- Add a keyless Air quality layer to the Weather group, with Environment and
+  Climate Change Canada's AQHI as the first registered provider. Readings carry
+  `{ provider, scale, value, band }` so another network can be added without
+  inventing a shared numeric meaning across indices that do not share one; the
+  row and readout both state that coverage is Canada only. The WEATHER card
+  shows the band legend and the highest readings currently in view. AQHI is
+  reported as an integer from 1 with an open-ended "10+", so readings round to
+  that published form rather than the decimal precision the API returns.
+  Readings older than six hours are dropped, and the layer reports `stale`
+  through `getStats()` (also when every observation was dropped) so feed
+  provenance cannot describe an aged feed as live. Voice can switch it on and
+  query readings by value, band, station and observation time.
+
 - Bound six upstream body reads (FIRMS CSV, CelesTrak TLE groups, adsb.lol
   `/v2/mil`, TomTom flow tiles, OpenSky `states/all` and adsbdb lookups) with
   streaming size caps that cancel the body at the cap or the route's deadline;