fix: make about page dynamic to prevent build-time token key mismatch

The about page was statically pre-rendered at build time using the
Dockerfile's dummy IMMICH_API_KEY. The portrait image token was
encrypted with sha256('build-placeholder') but decrypted at runtime
with sha256(real-key) → 400 Bad Request.

app/about/page.tsx

@@ -11,6 +11,8 @@ import { imageUrl, assetPlaceholder } from '@/lib/urls';
 import { immich } from '@/lib/immich';
 import './about.css';
 
+export const dynamic = 'force-dynamic';
+
 interface AboutFrontmatter {
   portrait?: string;
   name?: string;