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>

README.md

@@ -0,0 +1,92 @@
+# Planar EL512.256-H on ESP32
+
+Drive a Planar EL512.256-H (512 × 256, monochrome electroluminescent) panel from an
+ESP-WROOM-32 (classic ESP32), with an [Adafruit GFX](https://github.com/adafruit/Adafruit-GFX-Library)
+compatible driver so the usual drawing, text and font APIs work.
+
+The panel has no frame memory and needs a continuous video stream. The ESP32's I2S0
+peripheral in 8-bit parallel (LCD) mode streams a precomputed frame from DMA, so the
+CPU is free while the panel refreshes.
+
+**Status:** project skeleton. Framebuffer, GFX layer and row encoder are in place; the
+I2S/DMA start-up (`EL512Panel::startI2S()`) is still a stub.
+
+## Hardware
+
+- ESP-WROOM-32 dev board (`esp32dev`)
+- Planar EL512.256-H, configured for **two-bit parallel mode** (mode jumper OFF, see datasheet)
+- Datasheet: [docs/datasheet/EL512.256-H3 FRB.pdf](docs/datasheet/EL512.256-H3%20FRB.pdf)
+- Check the panel's logic-level and supply requirements in the datasheet before wiring.
+
+## Wiring
+
+| Panel signal | Function                                | ESP32 GPIO | DMA byte bit |
+|--------------|-----------------------------------------|-----------:|-------------:|
+| VCLK         | Video clock (rising edge)               | 18         | I2S clock    |
+| VID          | Pixel data, even columns                | 19         | 0            |
+| TVID         | Pixel data, odd columns (two-bit mode)  | 21         | 1            |
+| HS           | Horizontal sync                         | 22         | 2            |
+| VS           | Vertical sync                           | 23         | 3            |
+| ENABLE       | Display enable                          | 25         | —            |
+| _LOWPWR      | Low-power mode (active low)             | 26         | —            |
+| GND          | Ground                                  | GND        | —            |
+
+The pin map lives in [include/pins.h](include/pins.h).
+
+## Timing
+
+| Parameter            | Value                                   |
+|----------------------|-----------------------------------------|
+| Pixel clock (VCLK)   | 5 MHz, 2 pixels per clock               |
+| Clocks per row       | 272 (256 data + 16 blanking)            |
+| Lines per frame      | 261 (256 visible + 5 blanking)          |
+| Refresh              | 5 MHz / (272 × 261) ≈ 70.4 Hz           |
+
+## Layout
+
+```
+platformio.ini        build config (esp32dev, Arduino, Adafruit GFX)
+include/pins.h        pin map
+src/main.cpp          test sketch: test pattern + text
+lib/EL512/            local library
+  src/EL512Panel.*    framebuffer, row encoder, I2S DMA refresh (stub)
+  src/EL512_GFX.*     Adafruit_GFX subclass
+test/                 unit tests (placeholder)
+docs/                 datasheet and notes
+```
+
+## Build and flash
+
+Requires [PlatformIO](https://platformio.org/) (CLI or the VS Code extension).
+
+```bash
+pio run
+```
+
+```bash
+pio run -t upload
+```
+
+```bash
+pio device monitor
+```
+
+## Using the driver
+
+```cpp
+#include <EL512.h>
+#include "pins.h"
+
+EL512Panel panel({el512pins::VCLK, el512pins::VID, el512pins::TVID, el512pins::HS,
+                  el512pins::VS, el512pins::ENABLE, el512pins::LOWPWR_N});
+EL512_GFX display(panel);
+
+void setup() {
+  display.begin();
+  display.setTextColor(1);
+  display.print("Hello");
+  display.display();   // push the drawing buffer to the refresh stream
+}
+```
+
+See [docs/README.md](docs/README.md) for design notes and the plan.