After orientation detection, the frontend now automatically calls the
page-split endpoint. When a double-page book spread is detected, two
sub-sessions are created and each goes through the full pipeline
(deskew/dewarp/crop) independently — essential because each page of a
spread tilts differently due to the spine.
Frontend changes:
- StepOrientation: calls POST /page-split after orientation, shows
split info ("Doppelseite erkannt"), notifies parent of sub-sessions
- page.tsx: distinguishes page-split sub-sessions (current_step < 5)
from crop-based sub-sessions (current_step >= 5). Page-split subs
only skip orientation, not deskew/dewarp/crop.
- page.tsx: handleOrientationComplete opens first sub-session when
page-split was detected
Backend changes (orientation_crop_api.py):
- page-split endpoint falls back to original image when orientation
rotated a landscape spread to portrait
- start_step parameter: 1 if split from original, 2 if from oriented
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>