Fix 3.5" black screen: drive backlight on GPIO27, not GPIO21.

GPIO21 is GT911 INT on 3248S035C; PWM on the wrong pin left the panel dark.

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

firmware/cyd_35r/VERSION.txt

@@ -1,15 +1,11 @@
 name: CYD temperature (cyd_35r)
-git: de177b2
+git: 0a1b612
 date: 2026-10-25
-board: ESP32-3248S035 (ST7796)
+board: ESP32-3248S035 (ST7796 + GT911)
 flash_size: 4MB
 offsets:
   0x1000  bootloader.bin
   0x8000  partitions.bin
   0xe000  boot_app0.bin
   0x10000 firmware.bin
-sha256:
-  bootloader.bin  3D234A7471F67B013686DABD4DEE7C1FA915C9928463616A94BC9297ACF1ABF8
-  boot_app0.bin   F94C5D786A7A8FAB06AC5D10E33BF37711A6697636DC037559EA19CC410A17F0
-  firmware.bin    A8033223DDE79874B4CA41AFE3DBB247938184123FB66BCAA6EAF7F5C1D32516
-  partitions.bin  0A8B5720E7B77FF11F1462458C3A509DEE79224E5279898F26D6A2E3AE0517B7
+note: TFT_BL=GPIO27

firmware/export_from_build.ps1

@@ -73,8 +73,8 @@ if (Test-Path $metaPath) {
   try {
     $meta = Get-Content $metaPath -Raw | ConvertFrom-Json
     $meta.boardId = $boardIdHint
-    if ($Env -eq "cyd_35r" -and $meta.name -notmatch "3\.5") {
-      $meta.name = ($meta.name -replace "\s*$","") + " (3.5\")"
+    if ($Env -eq "cyd_35r" -and $meta.name -notmatch '3\.5') {
+      $meta.name = ($meta.name -replace '\s*$','') + ' (3.5")'
     }
     $meta | ConvertTo-Json -Depth 8 | Set-Content -Encoding utf8 $metaPath
   } catch {