fix(board): fix container void/overflow gap across scrollable and collapse states (#6750)

A container's outer grid cell and its own inner content grid are sized by
two independent calculations that only agree when the container is
scrollable and expanded. When collapsed, or when non-scrollable content
needs more rows than declared, the inner grid keeps rendering at its old/
content-driven size while the outer cell shrinks or stays fixed, leaving
an invisible-but-space-occupying box that inflates the board's scroll
height into a visible empty gap below the container.

Pass the outer instance's collapsed row count down as a
viewportRowCountOverride so the inner grid matches it exactly when
collapsed, and grow the outer placement's height to the already-computed
content minimum (getContainerMinimumSizes) for non-scrollable containers
so it stays in sync with the inner grid's own growth.

apps/nextjs/src/components/board/sections/container-section.tsx

@@ -8,6 +8,7 @@ import { useEditMode } from "@homarr/boards/edit-mode";
 import { useI18n } from "@homarr/translation/client";
 
 import type { ContainerSectionItem } from "~/app/[locale]/boards/_types";
+import { COLLAPSED_SECTION_ROW_COUNT } from "~/components/board/layout";
 import { SectionGrid } from "./grid/section-grid";
 import { useSectionCollapse } from "./section-collapse";
 import { useOpenSectionApps } from "./use-open-section-apps";
@@ -149,7 +150,13 @@ export const BoardContainerSection = ({ section }: Props) => {
           aria-hidden={isVisuallyCollapsed}
           inert={isVisuallyCollapsed}
         >
-          <SectionGrid section={section} columnCount={section.width} requestedRowCount={section.height} label={label} />
+          <SectionGrid
+            section={section}
+            columnCount={section.width}
+            requestedRowCount={section.height}
+            viewportRowCountOverride={isVisuallyCollapsed ? COLLAPSED_SECTION_ROW_COUNT : undefined}
+            label={label}
+          />
         </Box>
       </Card>
       {isEditMode && <BoardContainerMenu section={section} />}