Add native address search with geocoding for location presets, remove itilog.com link

Adds a new AddressSearchScreen: enter an address on a dedicated
keyboard (with a special-character page for common European accented
letters), geocode it via the free OpenStreetMap Nominatim service,
confirm the found place, optionally name it, and save it as a new
location preset - no external website needed anymore.

Reachable both from Location Presets > "+" (choice between "by
address" and manual coordinates) and, for new users, from a one-time
FirstRunLocationScreen shown right after the language picker on first
boot, explaining why an exact address beats automatic IP geolocation
and letting them set it up immediately (skippable).

Removes the itilog.com link/tip added in the previous commit (Location
Presets info screen, all 6 languages, and the README) - superseded by
this native in-app flow.

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

src/config.h

@@ -24,6 +24,13 @@ namespace Config {
     constexpr const char* IP_GEO_HOST = "ip-api.com";
     constexpr const char* IP_GEO_PATH = "/json/?fields=status,lat,lon,offset,countryCode";
 
+    // Adresssuche (AddressSearchScreen) - kostenloser, anmeldefreier
+    // Geokodierungs-Dienst (OpenStreetMap Nominatim). Deren Nutzungsregeln
+    // verlangen einen aussagekraeftigen User-Agent statt des HTTPClient-
+    // Standardwerts, siehe https://operations.osmfoundation.org/policies/nominatim/.
+    constexpr const char* NOMINATIM_HOST = "nominatim.openstreetmap.org";
+    constexpr const char* NOMINATIM_USER_AGENT = "EiswolfsFlightradarCYD (github.com/Eiswolf-BG/eiswolfs-flightradar-CYD)";
+
     struct GpsPinPair { uint8_t rx; uint8_t tx; const char* label; };
     constexpr GpsPinPair GPS_PIN_CANDIDATES[] = {
         {22, 27, "G22/G27"}