z-index audit + aperture fill + resize:end debounce + landscape sig-grid cap

- #id_aperture_fill: position:fixed→absolute (clips to .room-page, avoids h2/navbar);
  z-index 105→90 (below blur backdrops at z-100); landscape override removed (inset:0 works both orientations)
- _base.scss: landscape footer z-index:100 (matches navbar); corrects unset z-index
- _room.scss: fix stale "navbar z-300" comment; landscape sig-deck-grid columns
  repeat(9,1fr)→repeat(9,minmax(0,90px)) to cap card size on wide viewports
- room.js: add resize:end listeners for scaleTable + sizeSigModal; new IIFE dispatches
  resize:end 500ms after resize stops so both functions re-measure settled layout
- tray.js: extract _reposition() from inline resize handler; wire to both resize and
  resize:end so tray repositions correctly after rapid resize or orientation change

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/static_src/scss/_base.scss

@@ -326,6 +326,7 @@ body {
         border-left: 0.1rem solid rgba(var(--secUser), 0.3);
         padding: 1rem 0;
         gap: 0;
+        z-index: 100;
 
         #id_footer_nav {
             flex-direction: column-reverse;