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>

src/operation.h

@@ -160,19 +160,6 @@ void normal_operation_impl(const String& mac, HTTP& http, const String& url, Pre
         http.addHeader("X-Just-Provisioned", "1");
     }
 
-    // Recovery handshake: drawNeeded survives a power-loss-during-draw
-    // because we set it before kicking the e-ink refresh and only clear
-    // it after the panel finishes. Telling the server about it lets it
-    // suppress rotation advancement (including the X-Boot-Reason: cold
-    // force-resync) so we get the SAME image back and can repaint it
-    // from the cached /img.bin, instead of chasing a fresh image every
-    // time a draw resets. Without this, cold-boot rotation defeats the
-    // 304-with-drawNeeded recovery branch and the device churns through
-    // images, leaving torn frames on the panel.
-    if (drawNeeded) {
-        http.addHeader("X-Draw-Pending", "1");
-    }
-
     const char* collectHeaders[] = { "X-Interval-Ms", "X-Image-Id", "X-Image-Sha256", "X-Claimed" };
     http.collectHeaders(collectHeaders, 4);
     int code = http.GET();