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/clocks.h

@@ -52,6 +52,7 @@
    ZM1500_ESP32 (CURRENTLY ACTIVE, CLOCK_72 below) -> ZM1500.ino
    WORDCLOCK                              -> wordclock.ino (+ font5x7.h for its scrolling/overlay font)
    DUMMY                                  -> dummy.ino (sensor-only "clock", no physical display)
+   NIXIE595_MULTIPLEX (CLOCK_90)          -> nixie595.ino
 */
 
 //#define CLOCK_1   //8266, UNFI PCB clock, 4x IN-16 tubes
@@ -110,11 +111,43 @@
 //#define CLOCK_57A  //V2-WROOM ESP32, UNFI 2xHV5222 6xZ57xM clock  /flat panel
 //#define CLOCK_70   //1 tube esp8266 Nixie Clock by UNFI
 //#define CLOCK_71   //2x VQC10 clock by UNFI
-#define CLOCK_72   //ESP32, UNFI board, ZM1500
+//#define CLOCK_72   //ESP32, UNFI board, ZM1500
 //#define CLOCK_80   //word clock, english version
 //#define CLOCK_81   //word clock, german version
 //#define CLOCK_82   //word clock, hungarian version
 //#define CLOCK_99   //Dummy clock, sensor box with MQTT connector
+#define CLOCK_90   //8266, RetroModding NixieIN12v2 HV2.0 (5 V): 4x IN-12, 2x IN-3, 2x 74HC595 multiplex
+
+#ifdef CLOCK_90   //8266, RetroModding NixieIN12v2 HV2.0 (5 V): 4x IN-12, 2x IN-3, 2x 74HC595 multiplex
+// Pins and shift-register bit map confirmed from the stock firmware SV1.3
+// (docs/stock-firmware-pins.md in the nixie-clock repo).
+#define DEBUG
+#define FW "fw90"  //firmware name
+#define MAXBRIGHTNESS 100
+#define NIXIE595_MULTIPLEX
+#define PIN_LATCH 15          //74HC595 storage clock. DATA = GPIO13 (HSPI MOSI), CLOCK = GPIO14 (HSPI SCK)
+#define SPI_FREQ 4000000      //stock uses 25 MHz; 16 bits per slot need far less
+byte anodeBits[] = {14, 13, 12, 11};   //595 word bit of each tube's anode: position 0 = rightmost (A4) ... 3 = leftmost (A1)
+#define NEON_BITS (1 << 10)   //IN-3 dots on P1. P2 (bit 15) drives the IN-12B decimal points on this board (JP2 closed)
+#define NEON_POS 1            //the dots are lit in this tube's multiplex slot, as on stock
+#define USE_NEOPIXEL
+#define NEOPIXEL_PIN 12       //bit-banged, GRB 800 kHz
+byte tubePixels[] = {0, 0, 1, 1, 2, 2, 3, 3};   //8 WS2812, two per tube (strip order not verified yet)
+#define USE_RTC               //DS3231 on I2C, detected at startup (address 0x68); the stock firmware never used it
+#define PIN_SDA 4
+#define PIN_SCL 5
+#define LIGHT_SENSOR_PIN A0   //LDR to Vcc, 10k to GND (REF_RESISTANCE default)
+#define MAXIMUM_LUX 100       //Lux level for maximum tube brightness
+#define AP_NAME "UNICLOCK"
+#define AP_PASSWORD ""
+#define WEBNAME "IN-12 Nixie Clock"
+#define FIRMWARE_SERVER ""    //no web-triggered HTTP update; use ArduinoOTA
+#define USE_ARDUINO_OTA
+#define OTA_HOSTNAME "nixie-in12"
+#if __has_include("secrets.h")
+  #include "secrets.h"        //optional, gitignored: DEFAULT_SSID, DEFAULT_PSW, OTA_PASSWORD (see secrets.h.example)
+#endif
+#endif
 
 //______________________ESP8266 CLOCKS by UNFI and GP ______________________________________________________
 #ifdef CLOCK_1   //8266, UNFI PCB clock, 4x IN-16 tubes