feat: visual layout editor for check field positioning

- SVG canvas showing all layout fields scaled to check dimensions
- Click or dropdown to select a field; drag to reposition
- Sidebar shows X/Y coordinates in decimal inches with fraction
  equivalents (¼", ½", ¹⁄₁₆", etc.)
- End X/Y inputs appear for Line and Graph fields
- Nudge buttons move selected field by ¹⁄₁₆" per click
- Auto-saves on drag end; debounced save on input/nudge changes
- Visible toggle hides fields from PDF without deleting them
- Admin-only Reset to Default wipes and re-seeds the layout
- Accessible to editor+ role via ⊞ button in account header

public/css/style.css

@@ -88,6 +88,10 @@ header {
 }
 
 .modal-wide { width: min(720px, 96vw); }
+.modal-layout-editor { width: min(980px, 96vw); }
+.layout-editor-body { flex-direction: row !important; padding: 0 !important; gap: 0; overflow: hidden; min-height: 340px; }
+#layout-canvas-container { flex: 1; min-width: 0; padding: 12px; overflow: hidden; background: var(--bg); }
+#layout-sidebar { width: 200px; flex-shrink: 0; padding: 12px; border-left: 1px solid var(--border); display: flex; flex-direction: column; gap: 10px; overflow-y: auto; background: var(--surface); }
 
 .qbo-tabs {
   display: flex;