Add OTA firmware update via GitHub Releases API

New "Check for update" entry in Menu > System checks the latest
GitHub release's tag against the running version and, if newer,
downloads and flashes its firmware.bin asset directly over WiFi -
no cable or web flasher needed. Requires switching the partition
scheme to min_spiffs (two OTA-capable app partitions instead of a
single non-OTA one), which needs a full reflash.

confirmWarningScreen() now takes title/body as strings instead of
StringIds so it can show a dynamically composed message (the target
version number) for the update confirmation, with an accent color
parameter so the OTA confirmation can use green instead of the
red used for the existing destructive-action confirmations.

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

src/ota_update.cpp

@@ -0,0 +1,107 @@
+#include "ota_update.h"
+#include "config.h"
+#include <WiFiClientSecure.h>
+#include <HTTPClient.h>
+#include <HTTPUpdate.h>
+#include <ArduinoJson.h>
+#include <cstdlib>
+#include <cstdio>
+#include <cstring>
+
+namespace OtaUpdate {
+
+namespace {
+    constexpr const char* RELEASES_API_URL =
+        "https://api.github.com/repos/Eiswolf-BG/eiswolfs-flightradar-CYD/releases/latest";
+    // GitHub verlangt bei API-Anfragen einen aussagekraeftigen User-Agent
+    // (sonst HTTP 403) - gleiches Prinzip wie Config::NOMINATIM_USER_AGENT
+    // fuer die Adresssuche.
+    constexpr const char* USER_AGENT =
+        "EiswolfsFlightradarCYD-OTA/1.0 (+https://github.com/Eiswolf-BG/eiswolfs-flightradar-CYD)";
+
+    bool parseVersion(const char* s, int& major, int& minor, int& patch) {
+        major = minor = patch = 0;
+        if (!s || !s[0]) return false;
+        if (s[0] == 'v' || s[0] == 'V') s++;
+        return sscanf(s, "%d.%d.%d", &major, &minor, &patch) == 3;
+    }
+
+    // > 0 wenn a neuer als b, 0 wenn gleich, < 0 wenn a aelter als b.
+    // Bewusst eine echte numerische Versionsvergleich statt eines simplen
+    // String-Vergleichs (der wuerde z.B. "3.10.0" faelschlich als "kleiner"
+    // als "3.9.0" einordnen).
+    int compareVersions(const char* a, const char* b) {
+        int aMaj, aMin, aPat, bMaj, bMin, bPat;
+        if (!parseVersion(a, aMaj, aMin, aPat) || !parseVersion(b, bMaj, bMin, bPat)) return 0;
+        if (aMaj != bMaj) return aMaj - bMaj;
+        if (aMin != bMin) return aMin - bMin;
+        return aPat - bPat;
+    }
+}
+
+CheckInfo checkForUpdate() {
+    CheckInfo info;
+
+    WiFiClientSecure client;
+    client.setInsecure();
+    client.setTimeout(8000);
+
+    HTTPClient http;
+    http.setTimeout(8000);
+    if (!http.begin(client, RELEASES_API_URL)) return info;
+    http.addHeader("User-Agent", USER_AGENT);
+
+    int code = http.GET();
+    if (code != HTTP_CODE_OK) {
+        http.end();
+        return info;
+    }
+    String body = http.getString();
+    http.end();
+
+    JsonDocument doc;
+    if (deserializeJson(doc, body)) return info;
+
+    const char* tag = doc["tag_name"] | "";
+    if (!tag[0]) return info;
+
+    strncpy(info.latestVersion, (tag[0] == 'v' || tag[0] == 'V') ? tag + 1 : tag,
+            sizeof(info.latestVersion) - 1);
+
+    JsonArray assets = doc["assets"];
+    for (JsonObject asset : assets) {
+        const char* name = asset["name"] | "";
+        if (strcmp(name, "firmware.bin") == 0) {
+            const char* url = asset["browser_download_url"] | "";
+            strncpy(info.downloadUrl, url, sizeof(info.downloadUrl) - 1);
+            break;
+        }
+    }
+
+    if (!info.downloadUrl[0]) return info; // Release ohne firmware.bin-Anhang
+
+    int cmp = compareVersions(info.latestVersion, Config::APP_VERSION);
+    info.result = (cmp > 0) ? CheckResult::UpdateAvailable : CheckResult::UpToDate;
+    return info;
+}
+
+bool performUpdate(const char* url, void (*onProgress)(uint8_t percent)) {
+    WiFiClientSecure client;
+    client.setInsecure();
+    client.setTimeout(15000);
+
+    // Wir zeigen nach erfolgreicher Installation selbst noch eine kurze
+    // Erfolgsmeldung an, bevor das Geraet neu startet - siehe
+    // menu_screen.cpp::runOtaUpdateScreen().
+    httpUpdate.rebootOnUpdate(false);
+    httpUpdate.onProgress([onProgress](int cur, int total) {
+        if (onProgress && total > 0) {
+            onProgress((uint8_t)((cur * 100) / total));
+        }
+    });
+
+    t_httpUpdate_return result = httpUpdate.update(client, url);
+    return result == HTTP_UPDATE_OK;
+}
+
+}