Add LCD1602A I2C test with SoftSPI touch and LVGL.

PCF8574 backpack on SDA=GPIO22/SCL=GPIO27, demo/hello/clear/backlight UI, and flashable firmware/cyd package.

Co-authored-by: Cursor <cursoragent@cursor.com>

include/lcd.h

@@ -0,0 +1,20 @@
+#pragma once
+
+#include <stddef.h>
+#include <stdint.h>
+
+void lcd_init();
+
+bool lcd_ok();
+uint8_t lcd_addr();
+
+void lcd_set_backlight(bool on);
+bool lcd_backlight();
+
+void lcd_clear();
+void lcd_set_line(uint8_t row, const char *text);
+void lcd_get_line(uint8_t row, char *out, size_t out_len);
+
+/** 写入两行示例文案并点亮背光 */
+void lcd_demo(uint8_t index);
+uint8_t lcd_demo_count();