fix(build): add prerender entry for /hilfe/transkription

The SvelteKit prerender crawler cannot reach this route because
hooks.server.ts redirects all non-public paths to /login before the
crawler follows links. Explicitly listing the route in kit.prerender.entries
tells SvelteKit to render it directly without crawling.

Also removes a misleading comment that claimed the auth hook guards
prerendered static files — it does not. Prerendered HTML is served as a
static file by the reverse proxy; hooks.server.ts only runs for SSR requests.

Closes #472

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

frontend/src/routes/hilfe/transkription/+page.ts

@@ -1,3 +1 @@
-// Safe: handleAuth in hooks.server.ts redirects unauthenticated requests
-// before prerendered HTML is visible.
 export const prerender = true;