StepUpload now has 3 phases:
1. File selection: drop zone / file picker → shows preview
2. Review: title input, category, file info → "Hochladen" button
3. Uploaded: shows session image → "Weiter" button
No more auto-advance after upload. User controls every step.
openSession() removed from onUploaded callback to prevent
step-reset race condition.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
469f09d1e1