feat: add internal_component block type with contact form

InternalComponentBlock dispatches on `component` field value.
ContactFormComponent submits via /api/contact (SvelteKit proxy →
CMS /api/forms/kontakt/submit) with honeypot + client_age_ms.
BlockRenderer and block-types.ts updated accordingly.

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

src/lib/block-types.ts

@@ -422,6 +422,17 @@ export type CalendarBlockData = Omit<
   layout?: BlockLayout;
 };
 
+/** Internal component block (_type: "internal_component"). */
+export type InternalComponentId = "form-contact";
+
+export interface InternalComponentBlockData {
+  _type?: "internal_component";
+  _slug?: string;
+  id?: string;
+  component?: InternalComponentId;
+  layout?: BlockLayout;
+}
+
 export interface WindMapBlockData {
   _type?: "wind_map";
   _slug?: string;