fix: resolve compiler warnings (from PR #8 by @waltje)

- weather.cpp: StaticJsonDocument → JsonDocument (ArduinoJson v7 API)
- display.cpp: daylightStr buffer 16 → 32 bytes (suppress GCC sprintf warning)
- ntp_client.cpp: remove unused weekday variable

Applied manually due to repo layout mismatch in original PR.

Co-authored-by: waltje <waltje@users.noreply.github.com>
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

firmware/clock_ntp_ota_v1.9/display.cpp

@@ -168,7 +168,7 @@ void ICACHE_FLASH_ATTR displaySunTimes() {
   int daylightHours = daylightMinutes / 60;
   int daylightMins = daylightMinutes % 60;
 
-  char daylightStr[16];
+  char daylightStr[32];
   sprintf(daylightStr, "Day %dh %dm", daylightHours, daylightMins);
 
   display.setTextSize(1);

firmware/clock_ntp_ota_v1.9/ntp_client.cpp

@@ -16,7 +16,6 @@ bool ICACHE_FLASH_ATTR isDST(unsigned long epochTime) {
 
   int month = timeinfo->tm_mon + 1; // 1-12
   int day = timeinfo->tm_mday;      // 1-31
-  int weekday = timeinfo->tm_wday;  // 0=Sunday
   int hour = timeinfo->tm_hour;
 
   // Not DST: November - February

firmware/clock_ntp_ota_v1.9/weather.cpp

@@ -28,7 +28,7 @@ void ICACHE_FLASH_ATTR onWeatherResponse(void* optParm, AsyncHTTPRequest* reques
       Serial.printf("Weather response: %d bytes\n", payload.length());
 
       // Parse JSON response
-      StaticJsonDocument<1536> doc;
+      JsonDocument doc;
       DeserializationError error = deserializeJson(doc, payload);
 
       if (!error) {