Revert "fix(13e6): X-Draw-Pending recovery handshake + CDC serial routing"

This reverts commit 3d7a793. The X-Draw-Pending header suppresses
rotation server-side whenever the firmware boots with NVS_KEY_DRAW_NEEDED
set — including overriding the cold-boot force-resync. If drawNeeded ever
gets stuck (e.g. an interrupted draw whose recovery branch itself fails),
the picture stops advancing entirely. Reverting until we have telemetry
confirming whether that flag is being asserted in the field; the bare
304-with-drawNeeded recovery branch alone is sufficient for the typical
power-loss-mid-draw case.

ARDUINO_USB_CDC_ON_BOOT=1 was bundled in the same commit and goes with
it — losing USB-serial visibility on the 13.3" until we re-add it cleanly.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

platformio.ini

@@ -126,13 +126,6 @@ build_flags =
     -DPIN_PWR=1
     -DPANEL_ID=\"waveshare-13.3-spectra6\"
     -DBOARD_HAS_PSRAM
-    ; Route Serial through the S3's native USB-CDC. Without this the default
-    ; arduino-esp32 routing sends Serial to UART0, whose pins aren't wired to
-    ; either USB endpoint on the 13.3E6 board — making firmware logs invisible
-    ; over USB and forcing reliance on server-side telemetry alone. The CDC
-    ; endpoint enumerates as the "Espressif USB JTAG serial debug unit" ACM
-    ; port; it disappears when the chip deep-sleeps and re-enumerates on wake.
-    -DARDUINO_USB_CDC_ON_BOOT=1
 lib_deps =
     ricmoo/QRCode@^0.0.1