v2.8.0: Weather icon in header

Adds a small weather icon in the header, right where the old camera
button used to be. Shows current conditions (sun, cloud,
sun-behind-cloud, rain, snow, thunderstorm) for whichever location is
currently active, including active location presets, so switching to
e.g. Milan shows Milan's weather. Powered by the free Open-Meteo API
(no API key needed), refreshed automatically every 10 minutes in the
background, or immediately after switching to a different location
preset. Icons are drawn entirely with TFT_eSPI basic shapes (circles,
lines), no image files or extra fonts needed.

The initial implementation failed to parse Open-Meteo's response
(ArduinoJson "InvalidInput") because the API replies with
Transfer-Encoding: chunked and streaming directly from
http.getStream() didn't reassemble the chunks correctly. Fixed by
collecting the full body via http.getString() first, then parsing
that.

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

src/config.h

@@ -6,7 +6,7 @@ namespace Config {
     // CLAUDE.md-Workflow "Standard-Workflow: Push & Release") - erscheint
     // im Info-Screen (Menue > System > Info) und muss zum jeweiligen
     // Git-Tag passen.
-    constexpr const char* APP_VERSION = "2.7.5";
+    constexpr const char* APP_VERSION = "2.8.0";
 
     // Display-Helligkeit (Menue > System > Helligkeit), in Prozent.
     // MIN bewusst nicht 0 - ein komplett dunkles Display koennte sonst wie
@@ -40,6 +40,12 @@ namespace Config {
     constexpr uint32_t FETCH_INTERVAL_MS = 8000;
     constexpr uint32_t HTTP_TIMEOUT_MS = 6000;
 
+    // Wetter-Icon im Header (siehe weather.cpp) - deutlich seltener
+    // abgefragt als die ADS-B-Daten, das Wetter aendert sich nicht
+    // minuetlich und die kostenlose Open-Meteo-API soll nicht unnoetig oft
+    // belastet werden.
+    constexpr uint32_t WEATHER_FETCH_INTERVAL_MS = 600000; // 10 Minuten
+
     constexpr float DEFAULT_PROXIMITY_ALERT_KM = 8.0f;
 
     constexpr float LED_ALERT_RADIUS_KM = 3.0f;