ui: card-surface utility, rounded corners, calendar polish, banner layout

- Add .card-surface utility (@layer components): rounded-sm border shadow-sm
- Card.svelte, CalendarBlock, SearchableTextBlock, BlogOverview use card-surface
- OrganisationsBlock: logo h-12 rounded-sm, description style cleanup, pt-1 for hover clip fix
- DeadlineBanner: container-custom width constraint, text left-aligned
- WindAreaPanel stats: card-surface
- CalendarBlock: rounded-sm day headers, past days opacity-20 + diagonal strike
- Add .day-past pseudo-element utility for diagonal line

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

src/lib/components/blocks/OrganisationsBlock.svelte

@@ -64,12 +64,12 @@
 
 {#snippet defaultCard(o: OrganisationEntry, linkUrl: string | undefined, logoField: ReturnType<typeof organisationLogoField>, orgIndex: number)}
   <Card href={linkUrl} class="h-full">
-    <div class="flex h-11 w-11 shrink-0 items-center justify-center overflow-hidden bg-stein-100">
+    <div class="flex h-12 w-12 shrink-0 items-center justify-center overflow-hidden rounded-sm border border-stein-100 bg-stein-100">
       {#if logoField}
         <RustyImage
           src={logoField.url}
           focal={logoField.focal ?? null}
-          width={88}
+          width={96}
           aspect="1/1"
           fit="contain"
           quality={85}
@@ -98,9 +98,9 @@
         <Badge color={o.badge.color}>{o.badge.label}</Badge>
       </div>
     {/if}
-    <h5 class="mb-1 min-w-0 truncate text-sm font-medium leading-tight text-stein-900">{o.name ?? ""}</h5>
+    <h5 class="min-w-0 truncate text-sm font-medium leading-tight text-stein-900">{o.name ?? ""}</h5>
     {#if o.description}
-      <p class="line-clamp-2 text-xs font-light text-stein-600">{o.description}</p>
+      <p class="line-clamp-2 text-xs text-stein-500">{o.description}</p>
     {/if}
   </Card>
 {/snippet}
@@ -140,7 +140,7 @@
     <div class="relative">
       <div
         bind:this={scroller}
-        class="flex gap-4 overflow-x-auto scroll-smooth snap-x snap-mandatory pb-2 [scrollbar-width:thin]"
+        class="flex gap-4 overflow-x-auto scroll-smooth snap-x snap-mandatory pt-1 pb-2 [scrollbar-width:thin]"
       >
         {#each orgs as org, orgIndex}
           {#if typeof org === "object" && org !== null}