fix(portal): remove stray } in logo data URL and restore Dashboard redirect

- CustomerPortal.tsx: fix stray } in base64 data URL src attribute
- Dashboard.tsx: restore Navigate to /login for !sessionId (defense-in-depth)

The stray } was introduced in commit fa92a65 which also reverted
the Dashboard redirect. This commit restores both fixes.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/src/portal/CustomerPortal.tsx

@@ -260,7 +260,7 @@ export function CustomerPortal() {
           <div className="hidden md:flex items-center gap-3 px-6 py-5 border-b border-stone-100">
             {branding.logoBase64 && branding.logoMimeType ? (
               <img
-                src={`data:${branding.logoMimeType};base64,${branding.logoBase64}}`}
+                src={`data:${branding.logoMimeType};base64,${branding.logoBase64}`}
                 alt=""
                 className="w-10 h-10 rounded-xl object-contain"
               />