feat: Social-Media-Bild-Generator für Kalender-Termine

Neuer Endpoint /api/social/calendar/[slug] rendert Termin via satori +
resvg zu PNG. Formate: og (1200x630) und square (1080x1080).
Gebrandetes Layout mit Datum, Titel, Ort. Inter-Font lazy von gstatic,
10min In-Memory-Cache pro Slug+Format.

CalendarBlock: zwei Download-Buttons pro Termin (Bild quer / quadr.).

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

package.json

@@ -42,6 +42,7 @@
     "@fontsource-variable/rubik": "^5.2.8",
     "@fontsource/inter": "^5.2.8",
     "@iconify/svelte": "^5.2.1",
+    "@resvg/resvg-js": "^2.6.2",
     "@turf/buffer": "^7.3.5",
     "@types/leaflet": "^1.9.21",
     "blurhash": "^2.0.5",
@@ -50,6 +51,8 @@
     "marked": "^17.0.2",
     "qrcode": "^1.5.4",
     "sanitize-html": "^2.13.1",
+    "satori": "^0.26.0",
+    "satori-html": "^0.3.2",
     "sharp": "^0.34.5"
   },
   "type": "module"