Set up PlatformIO project for EL512.256-H on ESP32

PlatformIO skeleton (esp32dev, Arduino, Adafruit GFX) with a local EL512
library: EL512Panel (1 bpp framebuffer, two-bit-mode row encoder, I2S DMA
refresh stub) and EL512_GFX (Adafruit_GFX subclass). Adds a test sketch,
pin map, README with wiring and timing, and moves the datasheet to
docs/datasheet/.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

lib/EL512/library.json

@@ -0,0 +1,11 @@
+{
+  "name": "EL512",
+  "version": "0.1.0",
+  "description": "Planar EL512.256-H electroluminescent panel driver for ESP32 (I2S parallel DMA) with Adafruit GFX support",
+  "keywords": "display, electroluminescent, planar, el512, esp32, i2s, gfx",
+  "frameworks": "arduino",
+  "platforms": "espressif32",
+  "dependencies": {
+    "adafruit/Adafruit GFX Library": "*"
+  }
+}