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/platformio.ini

@@ -28,3 +28,10 @@ upload_resetmethod = ck
 monitor_port = COM7
 monitor_speed = 115200
 monitor_filters = esp8266_exception_decoder
+
+; Same firmware, uploaded over WiFi with ArduinoOTA (espota). Add --auth=<OTA_PASSWORD> to
+; upload_flags once secrets.h sets one.
+[env:nixie_in12_ota]
+extends = env:nixie_in12
+upload_protocol = espota
+upload_port = 10.1.1.97