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/weather.cpp

@@ -0,0 +1,103 @@
+#include "weather.h"
+#include "config.h"
+#include "location_manager.h"
+#include <WiFi.h>
+#include <WiFiClientSecure.h>
+#include <HTTPClient.h>
+#include <ArduinoJson.h>
+#include <math.h>
+
+namespace Weather {
+
+namespace {
+    WiFiClientSecure client;
+    bool clientConfigured = false;
+
+    Condition currentCondition = Condition::Unknown;
+    uint32_t lastFetchMs = 0;
+    double lastLat = 0;
+    double lastLon = 0;
+    bool hasLastLocation = false;
+
+    // Ordnet den WMO-Wettercode von Open-Meteo (Feld "weathercode", siehe
+    // https://open-meteo.com/en/docs) einer der wenigen Icon-Kategorien zu,
+    // die main.cpp zeichnen kann.
+    Condition conditionFromWmoCode(int code) {
+        if (code == 0) return Condition::Clear;
+        if (code == 1 || code == 2) return Condition::PartlyCloudy;
+        if (code == 3 || code == 45 || code == 48) return Condition::Cloudy;
+        if ((code >= 51 && code <= 67) || (code >= 80 && code <= 82)) return Condition::Rain;
+        if (code >= 71 && code <= 77) return Condition::Snow;
+        if (code >= 95) return Condition::Thunderstorm;
+        return Condition::Unknown;
+    }
+
+    void fetchNow(double lat, double lon) {
+        if (WiFi.status() != WL_CONNECTED) return;
+
+        if (!clientConfigured) {
+            client.setInsecure();
+            client.setTimeout(Config::HTTP_TIMEOUT_MS);
+            clientConfigured = true;
+        }
+
+        HTTPClient http;
+        char url[160];
+        snprintf(url, sizeof(url),
+                 "https://api.open-meteo.com/v1/forecast?latitude=%.4f&longitude=%.4f&current_weather=true",
+                 lat, lon);
+
+        http.setTimeout(Config::HTTP_TIMEOUT_MS);
+        if (!http.begin(client, url)) return;
+
+        int code = http.GET();
+        if (code != HTTP_CODE_OK) {
+            http.end();
+            return;
+        }
+
+        // Body erst komplett als String einsammeln (getString() kuemmert
+        // sich zuverlaessig um Chunked-Transfer-Encoding), statt direkt aus
+        // http.getStream() zu parsen - Letzteres scheiterte bei Open-Meteo
+        // zuverlaessig mit einem ArduinoJson-"InvalidInput"-Fehler.
+        String body = http.getString();
+        http.end();
+
+        JsonDocument doc;
+        DeserializationError err = deserializeJson(doc, body);
+        if (err) return;
+
+        int wmoCode = doc["current_weather"]["weathercode"] | -1;
+        if (wmoCode < 0) return;
+
+        currentCondition = conditionFromWmoCode(wmoCode);
+    }
+}
+
+void update() {
+    double lat = 0, lon = 0;
+    LocationManager::getHomeLocation(lat, lon);
+    if (lat == 0 && lon == 0) return;
+
+    // Deutliche Standort-Aenderung (z.B. anderes Standort-Preset aktiviert)
+    // - sofort neu abfragen statt bis zum naechsten regulaeren Intervall zu
+    // warten, damit das Icon nicht minutenlang das Wetter des alten
+    // Standorts zeigt.
+    bool locationChanged = !hasLastLocation ||
+                            fabs(lat - lastLat) > 0.01 || fabs(lon - lastLon) > 0.01;
+
+    uint32_t now = millis();
+    if (!locationChanged && (now - lastFetchMs < Config::WEATHER_FETCH_INTERVAL_MS)) {
+        return;
+    }
+
+    lastFetchMs = now;
+    lastLat = lat;
+    lastLon = lon;
+    hasLastLocation = true;
+    fetchNow(lat, lon);
+}
+
+Condition current() { return currentCondition; }
+
+}