Fixes: missing user_preferences column (use onboarding_dismissed column),
PDF endpoint return type branching, WeasyPrint system deps, solo pro
branding storage, screenshot size limit, supporting data PATCH endpoint,
ExportPreviewModal download-only mode, guides as React components,
illustration opacity and title size corrections, unknown guide slug handling.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
