Restructure into a single PlatformIO project with nano and esp32 targets

- Shared BROSE9323 driver in lib/, ESPSERIAL selected via build_flags
- Nano firmware in src/nano, ESP32 firmware in src/esp32
- Move WiFi/MQTT credentials to gitignored secrets.h (template provided)
- Pin home-assistant-integration to 2.1.0 from the registry
- Add esp32_usb environment for first flash / recovery
- Add READMEs and CLAUDE.md

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

archive/README.md

@@ -0,0 +1,8 @@
+# Archive
+
+Old sketches kept for reference. They are **not** built. The `.txt` extension keeps
+PlatformIO from compiling them.
+
+- `SerialAPI_nano_old.cpp.txt`: an earlier version of the Nano serial firmware, from
+  before the EEPROM timing and the default flip time were added.
+- `marquee_demo.cpp.txt`: a scrolling text (marquee) demo, including an umlaut test.

archive/SerialAPI_nano_old.cpp.txt

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+#include <Arduino.h>
+#include "BROSE9323.h"
+// fixes
+#include <SPI.h>
+#include <Adafruit_I2CDevice.h>
+
+BROSE9323 display(84, 19, 28);
+
+uint32_t refresh_at;
+const uint32_t REFRESH_TIME = 120000L;
+
+//#define DEBUG
+void setup() {
+	Serial.begin(115200);
+	display.begin();
+	delay(1000);
+	
+	display.fillScreen(1);
+	display.display();
+	display.fillScreen(0);
+	uint32_t t1 = millis();
+	display.display();
+	uint32_t t2 = millis();
+	Serial.println(t2 - t1);
+}
+
+uint8_t hex2dec(char c) {
+	if (c >= '0' && c <= '9') return c - '0';
+	if (c >= 'A' && c <= 'F') return c - 'A' + 10;
+	if (c >= 'a' && c <= 'f') return c - 'a' + 10;
+	return 0;
+}
+
+void loop() {
+	if (Serial.available()) {
+		char cmd = Serial.read();
+		switch (cmd) {
+			// Ignore CR
+			case 0x0A:
+				break;
+			// Draw Bitmap (must be n x 8 wide)
+			case 'b': case 'B': //BxxyywwhhcBITMAP (xx/ww = 8 bit hex x position/width; yy/hh = 8 bit y position/height; c = 0/1 color; BITMAP = bytes as hex)
+				{
+					// May lead to buffer overflow, you may need to segment the bitmap into multiple frames
+					// Or just use the ser pixel function
+					while (Serial.available() < 9) {
+						delay(1);
+					}
+					uint8_t x = (hex2dec(Serial.read()) << 4) | hex2dec(Serial.read());
+					uint8_t y = (hex2dec(Serial.read()) << 4) | hex2dec(Serial.read());
+					uint8_t w = (hex2dec(Serial.read()) << 4) | hex2dec(Serial.read());
+					if (w % 4) {
+						Serial.println("ERR: Invalid bitmap width (not dividable by 4)");
+						Serial.flush();
+						break;
+					}
+					uint8_t h = (hex2dec(Serial.read()) << 4) | hex2dec(Serial.read());
+					if (h == 0) {
+						Serial.println("ERR: Invalid bitmap height (0)");
+						Serial.flush();
+						break;
+					}
+					uint8_t c = Serial.read() - '0';
+					uint8_t b = 0;
+					for (uint8_t _y = 0; _y < h; _y++) {
+						for (uint8_t _x = 0; _x < w; _x++) {
+							if ((_x & 0x3) == 0) {
+								if (!Serial.available()) {
+									Serial.println("WARN: OUTOFMEM");
+								}
+								while (!Serial.available()) {
+									delay(1);
+								}
+								b = hex2dec(Serial.read());
+							}
+							if (b & (1 << (0x3 - (_x & 0x3)))) {
+								display.drawPixel(x + _x, y + _y, c);
+							}
+						}
+					}
+					break;
+				}
+			// Display
+			case 'd': case 'D': //D
+				{
+					display.display();
+					break;
+				}
+			// Fill Screen
+			case 'f': case 'F': //Fc (c = 0/1 color)
+				{
+					while (Serial.available() <= 2) {
+						delay(1);
+					}
+					display.fillScreen(Serial.read() - '0');
+					break;
+				}
+			// Print Text
+			case 'p': case 'P': // PxxyycsTEXT (xx = 8 bit hex x position; yy = 8 bit y position; c = 0/1 color; s = 1/2 size; TEXT = string, newline = escaped \\n)
+				{
+					delay(5);
+					while (Serial.available() <= 6) {
+						delay(1);
+					}
+					uint8_t x = (hex2dec(Serial.read()) << 4) | hex2dec(Serial.read());
+					uint8_t y = (hex2dec(Serial.read()) << 4) | hex2dec(Serial.read());
+					uint8_t c = Serial.read() - '0';
+					display.setCursor(x, y);
+					display.setTextColor(c, !c);
+					display.setTextSize(Serial.read() - '0');
+					while (true) {
+						if (!Serial.available()) {
+							delay(1);
+						}
+						if (Serial.peek() == '\n') break;
+						if (Serial.peek() == '\r') {Serial.read();continue;};
+						char c = Serial.read();
+						if (c == '\\' && Serial.peek() == 'n') {
+							display.println();
+							Serial.read();
+						} else {
+							display.write(c);
+						}
+					}
+					return;
+				}
+			// Return buffer (show pixels on console)
+			case 'r': case 'R': //R
+				{
+					display.printBuffer();
+					Serial.flush();
+					break;
+				}
+			// Set Pixel
+			case 'S':
+				display.setDirect(true);
+			case 's': // Sxxyyc (xx = 8 bit hex x position; y = 8 bit y position; c = 0/1 color)
+				{
+					while (Serial.available() <= 6) {
+						delay(1);
+					}
+					uint8_t x = (hex2dec(Serial.read()) << 4) | hex2dec(Serial.read());
+					uint8_t y = (hex2dec(Serial.read()) << 4) | hex2dec(Serial.read());
+					bool color = hex2dec(Serial.read());
+					display.drawPixel(x, y, color);
+					display.setDirect(false);
+					break;
+				}
+			// Set Timing
+			case 'T': case 't': // Tttt (ttt = decimal timing in us)
+				{
+					while (Serial.available() <= 6) {
+						delay(1);
+					}
+					uint16_t t = atoi(Serial.readStringUntil('\n').c_str());
+					display.setTiming(t);
+					break;
+				}
+			default:
+#ifdef DEBUG
+				Serial.print("0x");
+				Serial.print(cmd >> 4, HEX);
+				Serial.print(cmd & 3, HEX);
+				Serial.println(" - command not known.");
+				Serial.flush();
+#endif
+				break;
+		}
+	}
+	// Refresh content every REFRESH_TIME (by default 2 min)
+	if (refresh_at < millis()) {
+		refresh_at = millis() + REFRESH_TIME;
+		display.display(true);
+	}
+}

archive/marquee_demo.cpp.txt

@@ -0,0 +1,42 @@
+#include <Arduino.h>
+#include "BROSE9323.h"
+// fixes
+#include <SPI.h>
+#include <Adafruit_I2CDevice.h>
+
+BROSE9323 display(84, 19, 28);
+
+/*
+   UMLAUT:
+   Ä \x8E
+   ä \x84
+   Ö \x99
+   ö \x94
+   Ü \x9A
+   ü \x81
+   ß \xE0
+*/
+// const char text[] = "This is a test. Testing \x9Aml\x8Aute. ";
+const char text[] = "This is a test. Testing Ümläute. ";
+const uint8_t textsize = 2;
+
+void setup()
+{
+  display.begin();
+  delay(2000);
+  display.fillScreen(0);
+  display.setTextSize(textsize);
+  display.setTextWrap(false);
+  display.setTextColor(1, 0);
+  //display.setDirect(true); //when using setTextColor(1, 0) we don't need a separate display() and the text scrolls more evenly (on *328*)
+}
+
+void loop()
+{
+  for (int16_t x = display.width(); x > -((int16_t)strlen(text) * textsize * 6); x--)
+  {
+    display.setCursor(x, 0);
+    display.print(text);
+    display.display();
+  }
+}