Run ESP_UniClock on the NixieIN12v2 clock

Adds CLOCK_90 and the nixie595.ino driver: two 74HC595s on hardware
SPI (GPIO13/14, latch GPIO15), multiplexed from an IRAM-only timer1
ISR. Neon dots on P1; P2 is the decimal-point line on this board.

Also:
- NeoPixel on any ESP8266 pin via bit-bang (GPIO12), and take the pin
  back after SPI.begin() claimed it as MISO
- ArduinoOTA (USE_ARDUINO_OTA), with an OTA upload env in platformio.ini
- DST: EU end date (last Sunday of October) instead of the first Sunday
  of November, and recompute the time from the rules when DST is
  toggled instead of shifting it by 1 h
- forward declarations so PlatformIO's .ino conversion compiles
- FIRMWARE_SERVER can be overridden; empty for CLOCK_90

Verified on the clock: tubes, order, dots, LEDs, LDR, NTP time with DST.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

firmware/uniclock/ESP32_UniClock2/secrets.h.example

@@ -0,0 +1,6 @@
+// Copy to secrets.h (gitignored) and fill in. All entries are optional.
+// DEFAULT_SSID/DEFAULT_PSW are only applied on a factory reset (first boot with a new EEPROM layout);
+// otherwise set the WiFi from the clock's web page.
+#define DEFAULT_SSID ""
+#define DEFAULT_PSW ""
+#define OTA_PASSWORD ""   //ArduinoOTA password; remove the line for no password