Fix LCD1602 blank display: HD44780 timing, pinmap switch, contrast hint.

Match LiquidCrystal_I2C init delays; add Map button for alternate PCF8574 wiring; warn about blue contrast pot.

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

include/lcd.h

@@ -8,6 +8,11 @@ void lcd_init();
 bool lcd_ok();
 uint8_t lcd_addr();
 
+/** 0=标准 YwRobot(P0=RS..)，1=部分国产板(EN/RS 换脚) */
+uint8_t lcd_pinmap();
+void lcd_set_pinmap(uint8_t map);
+void lcd_reinit();
+
 void lcd_set_backlight(bool on);
 bool lcd_backlight();
 
@@ -15,6 +20,5 @@ 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();