landscape layout: remove max-width cutoff; sig-select stage/grid polish

- All landscape @media queries: drop and (max-width: 1440px) — sidebar layout
  now activates for all landscape orientations regardless of viewport width
- _base.scss landscape container: add max-width:none to override the
  @media(min-width:1200px) rule and fill the full space between sidebars
- sig-select sig-deck-grid: landscape now 9×2 @ 3rem cards; 18×1 at ≥1100px
  (bumped from 992px to avoid last-card clip); card text scales with --sig-card-w
- sig-stat-block: flex:1→flex:0 0 auto with width:--sig-card-w so it matches
  preview card dimensions instead of stretching across the full stage
- room.js sizeSigModal: landscape card width clamped to [90px, 160px]

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

src/static_src/scss/_dashboard.scss

@@ -149,7 +149,7 @@ body.page-dashboard {
     }
 }
 
-@media (orientation: landscape) and (max-width: 1440px) {
+@media (orientation: landscape) {
     // Reset the 666px min-width so #id_dash_content shrinks to fit within the
     // sidebar-bounded container rather than overflowing into the footer sidebar.
     #id_dash_content {