feat(calendar): CalendarCompact nutzt SectionHeader; fix IconButton-Typing

CalendarCompactBlock: plain h3 → SectionHeader (title + 'Alle kommenden Termine'-
Action). IconButton props via HTMLButton/AnchorAttributes statt Index-Signatur
(brach Storybook-Typing).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/components/blocks/CalendarCompactBlock.svelte

@@ -1,6 +1,6 @@
 <script lang="ts">
   import { getBlockLayoutClasses } from "$lib/block-layout";
-  import ArrowLink from "$lib/components/ArrowLink.svelte";
+  import SectionHeader from "$lib/components/SectionHeader.svelte";
   import type { CalendarBlockData, CalendarItemData } from "$lib/block-types";
   import { t as tStatic, T } from "$lib/translations";
   import type { Translations } from "$lib/translations";
@@ -81,13 +81,13 @@
   data-block-variant="compact"
   data-block-slug={block._slug}
 >
-  <div class="mb-2 flex items-baseline justify-between gap-4">
-    <h3 class="mb-0">{block.title ?? t(T.calendar_next_events)}</h3>
-    {#if linkHref()}
-      <div class="shrink-0">
-        <ArrowLink href={linkHref() ?? "#"} label={t(T.calendar_all_upcoming)} tone="wald" size="sm" />
-      </div>
-    {/if}
+  <div class="mb-4">
+    <SectionHeader
+      title={block.title ?? t(T.calendar_next_events)}
+      tag="h3"
+      actionLabel={linkHref() ? t(T.calendar_all_upcoming) : undefined}
+      actionHref={linkHref() ?? undefined}
+    />
   </div>
 
   {#if upcoming.length === 0}