refactor(consolidate): ArrowLink tone + FormSuccess-Komponente

A: ArrowLink um tone-Prop (himmel/wald/stein/white) — PostOverview + CalendarCompact
inline Arrow-Links → ArrowLink.
B: 3× identische Formular-Success-Boxen → internal/FormSuccess.svelte (rounded-lg).

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

src/lib/components/blocks/CalendarCompactBlock.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
   import { getBlockLayoutClasses } from "$lib/block-layout";
+  import ArrowLink from "$lib/components/ArrowLink.svelte";
   import type { CalendarBlockData, CalendarItemData } from "$lib/block-types";
   import { t as tStatic, T } from "$lib/translations";
   import type { Translations } from "$lib/translations";
@@ -83,13 +84,9 @@
   <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()}
-      <a
-        href={linkHref()}
-        class="inline-flex shrink-0 items-center gap-1 text-sm font-medium text-wald-700 no-underline hover:text-wald-800 hover:underline"
-      >
-        {t(T.calendar_all_upcoming)}
-        <span aria-hidden="true">→</span>
-      </a>
+      <div class="shrink-0">
+        <ArrowLink href={linkHref() ?? "#"} label={t(T.calendar_all_upcoming)} tone="wald" size="sm" />
+      </div>
     {/if}
   </div>