Split-pane editor: edit frames directly on the sheet

[ankitsejwal]

A desktop-first redesign of the editor. Instead of editing tiles above a separate preview, the page splits into a reorderable photo strip on the left and a sticky, always-visible print sheet on the right — and you edit each frame directly on the sheet.

What changed

• Edit on the sheet: click a frame to select it → drag the photo to reposition, scroll/slider to zoom, and edit the captions inline right on the frame. A contextual inspector bar holds orientation, zoom, remove and Done. Click empty sheet space to deselect.
• Left photo strip: compact reorderable thumbnails (drag handle), click to select, hover to remove, with the "Reading…" EXIF state.
• Global toolbar: location precision, date format, camera info, captions toggle and font moved into one top toolbar that applies to every frame.
• Always-on sheet: the sheet renders even with zero photos, so the "page" is permanently visible (the whole point). Sticky on lg+, and the layout collapses to a single stacked column on mobile.
• New editor-store holds the selected frame (kept separate so selection doesn't re-render every photo).
• Removed the old editing tile (Polaroid/PhotoGrid) and the now-dead "Frame size" control (it only ever styled that tile, never the sheet/PDF).

Verification (live, real browser)
Drove it via the chrome-devtools MCP against the dev server: confirmed selection ring + inspector + inline captions, the left strip stays in sync, multi-photo layout fills 3-per-row with cut marks, and the global toolbar drives every frame. typecheck / oxlint / build all green.

Nothing about the PDF/layout math changed, so the earlier headless guarantees (crop, orientation, paper, export) still hold.