feat(calendar): image/attachment per event, direct links, copy link, ImageModal component

- calendar_item schema: flyer → image (type: image), attachment (assetUrl)
- CalendarItemData: image + attachment fields
- event anchor IDs (#event-{slug}) with onMount hash scroll + auto-open
- share button uses direct calendar anchor URL
- copy link button (mdi:link-variant) copies anchor URL to clipboard
- ImageModal extracted as reusable component
- action buttons always show text (no expand-on-hover)
- onDestroy window guard (SSR fix)

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

src/lib/components/ImageModal.svelte

@@ -0,0 +1,44 @@
+<script lang="ts">
+    import { onMount, onDestroy } from "svelte";
+    import Icon from "@iconify/svelte";
+    import "$lib/iconify-offline";
+
+    let {
+        src,
+        alt = "",
+        onclose,
+    }: { src: string; alt?: string; onclose: () => void } = $props();
+
+    function onKeydown(e: KeyboardEvent) {
+        if (e.key === "Escape") onclose();
+    }
+
+    onMount(() => window.addEventListener("keydown", onKeydown));
+    onDestroy(() => {
+        if (typeof window !== "undefined")
+            window.removeEventListener("keydown", onKeydown);
+    });
+</script>
+
+<div
+    class="fixed inset-0 z-[9999] flex items-center justify-center bg-black/80 p-4 cursor-zoom-out"
+    onclick={onclose}
+    role="dialog"
+    aria-modal="true"
+    aria-label={alt || "Bild Vollansicht"}
+>
+    <img
+        {src}
+        {alt}
+        class="max-w-full max-h-full object-contain rounded shadow-2xl cursor-default"
+        onclick={(e) => e.stopPropagation()}
+    />
+    <button
+        type="button"
+        onclick={onclose}
+        class="absolute top-4 right-4 p-2 rounded-full bg-black/50 text-white hover:bg-black/70 transition-colors"
+        aria-label="Schließen"
+    >
+        <Icon icon="mdi:close" class="size-5" aria-hidden="true" />
+    </button>
+</div>