Add grid image system with multi-panel support and SPA routing
- Grid images: photograph component boxes in sub-sections, assemble
into one logical grid via perspective warp (homography)
- Source image gallery: bulk upload photos separately from grid setup
- Grid drafts: persist partial work, resume across sessions
- Multi-panel grids: define rows/cols per photo, system computes panel
layout; process partially configured grids, edit individual panels
- Pan/zoom canvas editor (HiDPI-aware, touch support) for corner alignment
- SPA routing with canonical URLs (history.pushState, server catch-all)
- Express error visibility: uncaughtException/unhandledRejection handlers
and 4-arg error middleware
- Original filename stored on source image upload
- Various null-safety fixes and CSS [hidden] override fixes
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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