Fix 3.5" backlight to GPIO27 and document CYD board pitfalls.

Align cyd_35r with 3248S035C pinout (BL!=INT) and point to CYD_PROJECT_GUIDE.

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

platformio.ini

@@ -54,19 +54,27 @@ build_flags =
 
 extra_scripts = pre:copy_lv_conf.py
 
-; Optional 3.5" CYD ESP32-3248S035 (ST7796 resistive). Default remains [env:cyd].
+; Optional 3.5" CYD ESP32-3248S035C (ST7796 + GT911 capacitive). Default [env:cyd].
 ; Build: pio run -e cyd_35r
+; Keep TOUCH_CS=-1 — GPIO33 is GT911 SDA, not resistive touch CS.
+; TFT_BL=GPIO27 (not 21 — 21 is GT911 INT). See ../CYD_PROJECT_GUIDE.md §1.1
 [env:cyd_35r]
 extends = env:cyd
+build_unflags =
+  -DILI9341_2_DRIVER=1
+  -DTFT_WIDTH=240
+  -DTFT_HEIGHT=320
+  -DTFT_BL=21
+  -DLV_MEM_SIZE=49152
 build_flags =
   ${env:cyd.build_flags}
-  -UILI9341_2_DRIVER
   -DST7796_DRIVER=1
-  -UTFT_WIDTH
-  -UTFT_HEIGHT
   -DTFT_WIDTH=320
   -DTFT_HEIGHT=480
-  -UTFT_BL
   -DTFT_BL=27
   -DCYD_BOARD_3248S035=1
+  -DUSE_HSPI_PORT
+  -DSUPPORT_TRANSACTIONS
+  -DTFT_RGB_ORDER=TFT_BGR
+  -DLV_MEM_SIZE=32768