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>

lib/BROSE9323/BROSE9323.h

@@ -0,0 +1,100 @@
+#ifndef BROSE9323_H
+#define BROSE9323_H
+
+#include <Adafruit_GFX.h>
+
+//#define FLIPDOT_PLCC_ADAPTER
+// ESPSERIAL is set per target via build_flags in platformio.ini (-D ESPSERIAL for the ESP32)
+
+const uint8_t _hannio_splash[] PROGMEM = {
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x39, 0xff, 0xff, 0xff, 0xff, 0xfe, 0x70,
+    0x3e, 0x00, 0x39, 0xff, 0xff, 0xff, 0xff, 0xfe, 0x70, 0xff, 0x00, 0x39, 0xff, 0xff, 0xff, 0xff,
+    0xfe, 0x71, 0xf7, 0xc0, 0x39, 0xff, 0xff, 0xff, 0xff, 0xfe, 0x73, 0xc1, 0xc0, 0x38, 0x1f, 0x87,
+    0xf0, 0x7f, 0x06, 0x73, 0x80, 0xe0, 0x38, 0x0f, 0x01, 0xc0, 0x3c, 0x02, 0x77, 0x7f, 0x60, 0x38,
+    0xc7, 0x78, 0xc6, 0x1c, 0x60, 0x77, 0x7f, 0x70, 0x39, 0xe3, 0xfc, 0xcf, 0x9c, 0xf8, 0x76, 0x00,
+    0x30, 0x39, 0xf3, 0xfc, 0xcf, 0x9c, 0xf8, 0x77, 0x7f, 0x70, 0x39, 0xf3, 0x80, 0xcf, 0x9c, 0xf8,
+    0x77, 0x7f, 0x60, 0x39, 0xf3, 0x00, 0xcf, 0x9c, 0xf8, 0x73, 0x80, 0xe0, 0x39, 0xf2, 0x3c, 0xcf,
+    0x9c, 0xf8, 0x73, 0xc1, 0xc0, 0x39, 0xf2, 0x7c, 0xcf, 0x9c, 0xf8, 0x71, 0xf7, 0xc0, 0x39, 0xf2,
+    0x3c, 0xcf, 0x9c, 0xf8, 0x70, 0xff, 0x80, 0x39, 0xf3, 0x00, 0xcf, 0x9c, 0xf8, 0x70, 0x3e, 0x00};
+
+class BROSE9323 : public Adafruit_GFX
+{
+private:
+    uint16_t _flip_time;
+    const uint8_t _panel_width;
+    const uint8_t _buffer_width;
+    const uint16_t _buffer_size;
+    uint8_t *_old_buffer = NULL;
+    uint8_t *_new_buffer = NULL;
+    bool _direct_mode = false;
+
+#ifdef ESPSERIAL
+    Stream *stream;
+#else
+    uint8_t _active_panel = 255;
+    uint8_t _active_col = 255;
+    uint8_t _active_row = 255;
+    bool _active_data;
+
+#ifndef FLIPDOT_PLCC_ADAPTER
+    const uint8_t ENABLE = 7,
+                  ADDR_0 = 3,
+                  ADDR_1 = 5,
+                  ADDR_2 = 6,
+                  COL_DATA = 4,
+                  COL_0 = 8,
+                  COL_1 = 10,
+                  COL_2 = 9,
+                  COL_3 = 11,
+                  COL_4 = 12,
+                  ROW_0 = A3,
+                  ROW_1 = A4,
+                  ROW_2 = A2,
+                  ROW_3 = A0,
+                  ROW_4 = A1,
+                  ROW_RESET = 13,
+                  ROW_SET = A5;
+#else
+    const uint8_t RELAY = 2,
+                  ENABLE = 3,
+                  ADDR_0 = 7,
+                  ADDR_1 = 6,
+                  ADDR_2 = 5,
+                  COL_DATA = 4,
+                  COL_0 = 12,
+                  COL_1 = 11,
+                  COL_2 = 10,
+                  COL_3 = 9,
+                  COL_4 = 8,
+                  ROW_0 = 13, //1 A1 CHECK
+        ROW_1 = A0,           //2 A2
+        ROW_2 = A1,           //4 A3
+        ROW_3 = A2,           //8 13 CHECK
+        ROW_4 = A3,           //F A0
+        ROW_RESET = A4,
+                  ROW_SET = A5;
+#endif
+
+    void _selectColumn(uint8_t);
+    void _selectPanel(uint8_t);
+    void _selectRow(uint8_t);
+    void _setData(bool);
+    void _strobe(void);
+#endif
+public:
+    BROSE9323(uint8_t, uint8_t, uint8_t, uint16_t ft = 280);
+#ifdef ESPSERIAL
+    void begin(Stream * = &Serial);
+#endif
+    void begin(void);
+    void display(bool force = false);
+    void drawPixel(int16_t x, int16_t y, uint16_t color);
+    void fillScreen(uint16_t);
+    void setDirect(bool);
+    void setTiming(uint16_t);
+#ifndef ESPSERIAL
+    void printBuffer(void);
+#endif
+    size_t print(const char *ifsh);
+};
+#endif //BROSE9323_H