feat(calendar): add feed subscription, bulk export, share & Google Cal

- /api/kalender.ics SSR route: ICS feed of all calendar items (webcal-subscribable, Cache 1h)
- buildICSFeed() / downloadICSFeed() for multi-event ICS export
- googleCalUrl() deep-link pre-fills Google Calendar create form
- Web Share API per event (navigator.share on mobile, clipboard fallback on desktop)
  — "Kopiert\!" toast per event for 2s after clipboard write
- Actions bar (subscribe + bulk export) only rendered after onMount
  — Apple platforms: webcal:// link opens Calendar.app natively
  — All others: direct ICS download via <a download>

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

src/routes/api/kalender.ics/+server.ts

@@ -0,0 +1,57 @@
+import type { RequestHandler } from '@sveltejs/kit';
+import { env } from '$env/dynamic/public';
+import { getCalendarItems } from '$lib/cms';
+import { buildICSFeed, type CalendarItemICS } from '$lib/calendar-ics';
+import type { CalendarItemData } from '$lib/block-types';
+
+function parseDate(iso: string | undefined | null): Date | null {
+  if (!iso) return null;
+  const d = new Date(iso);
+  return isNaN(d.getTime()) ? null : d;
+}
+
+function locationText(loc: unknown): string {
+  if (typeof loc === 'string') return loc;
+  if (loc && typeof loc === 'object') {
+    const t = (loc as { text?: unknown }).text;
+    if (typeof t === 'string') return t;
+  }
+  return '';
+}
+
+export const GET: RequestHandler = async () => {
+  const siteName = env.PUBLIC_SITE_NAME || 'Windwiderstand';
+
+  let rawItems: Awaited<ReturnType<typeof getCalendarItems>> = [];
+  try {
+    rawItems = await getCalendarItems();
+  } catch {
+    rawItems = [];
+  }
+
+  const icsItems: CalendarItemICS[] = rawItems
+    .flatMap((raw) => {
+      const item = raw as unknown as CalendarItemData;
+      const start = parseDate(item.terminZeit);
+      if (!start) return [];
+      const end = parseDate(item.terminEnde ?? null) ?? undefined;
+      const entry: CalendarItemICS = {
+        title: item.title || 'Termin',
+        start,
+        end,
+        description: (item as { description?: string }).description ?? undefined,
+        location: locationText((item as { location?: unknown }).location) || undefined,
+      };
+      return [entry];
+    });
+
+  const body = buildICSFeed(icsItems, `${siteName} – Termine`);
+
+  return new Response(body, {
+    headers: {
+      'Content-Type': 'text/calendar; charset=utf-8',
+      'Content-Disposition': 'inline; filename="windwiderstand-termine.ics"',
+      'Cache-Control': 'public, max-age=3600',
+    },
+  });
+};