Add WebUI live radar; mutex-protect AirlineFilter/AircraftWatchlist

The WebUI home page now shows a live radar canvas above the flight
logbook, polling a new /radar.json endpoint every 3 seconds. It
mirrors the device display: distance rings, aircraft colored by
altitude, ground vehicles as squares, rotorcraft as diamonds, and
emergency/watchlist/heavy-category rings in that priority. Applies
the same range, hide-ground-vehicles, and airline filters as the
device radar.

AirlineFilter and AircraftWatchlist gain proper mutex protection
around their in-memory arrays (previously only guarded around SD
file I/O) since the new /lists WebUI pages reach them from Core 0
(NetTask) in addition to their existing Core 1 (menu screen)
callers.

Note: the "notable aircraft" military/government callsign-prefix
marker is not implemented - Config::NOTABLE_CALLSIGN_PREFIXES was
never defined anywhere in this project, on the device display or
here. The "notable" ring currently fires on heavy-category aircraft
only.

Also documents the OTA-testing exception to the auto-flash rule in
CLAUDE.md (build-only during Push & Release, so the test device stays
on the previous version for OTA testing).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/i18n_fr.h

@@ -198,7 +198,7 @@ static const char* const I18N_FR[] = {
 
     "Journal / WebUI",
     "Journal / WebUI",
-    "Cette page web permet de consulter, télécharger et supprimer individuellement le journal de vol directement depuis un navigateur. Connecté au même réseau WiFi, ouvrez simplement un navigateur et allez à :",
+    "Cette page web affiche en haut un radar en direct avec tous les avions actuellement visibles, et en dessous permet de consulter, télécharger et supprimer individuellement le journal de vol directement depuis un navigateur. Connecté au même réseau WiFi, ouvrez simplement un navigateur et allez à :",
     "Pas de connexion WiFi - la page n'est accessible que lorsqu'une connexion réseau est établie.",
 
     "Météo",