feat(board): add SSR-compatible static grid for view mode

Split board rendering into two modes: a static CSS Grid for view mode
(SSR-friendly, no JS required for layout) and a lazy-loaded GridStack
for edit mode. This eliminates widget "pop-in" on page load by rendering
the full grid layout server-side.

apps/nextjs/src/styles/gridstack.scss

@@ -112,3 +112,17 @@
 .grid-stack-empty-wrapper {
   display: none !important;
 }
+
+.static-grid-container {
+  container-type: inline-size;
+}
+
+.static-grid-item-content {
+  position: absolute;
+  inset: 10px;
+
+  > .grid-stack-item-content {
+    width: 100%;
+    height: 100%;
+  }
+}