refactor: remove hotel-name fallback, fail fast when unconfigured

Drop the hardcoded FALLBACK_HOTEL_NAME ("Atom") preset and the brand.ts
module. HOTEL_NAME is now a required env var: if it (and the CMS hotel_name
setting) is missing the site fails validation at startup/build with a clear
message instead of silently rendering a placeholder hotel name.

resolveHotelName() resolves CMS hotel_name -> required HOTEL_NAME only.
Callers that used the preset (api/home route catch branch, CMS settings form
default, mobile-nav/logo-generator prop defaults) now use the configured name
or an empty default; the real name is already passed in by server parents.

src/components/public/logo-generator.tsx

@@ -16,10 +16,9 @@ import {
 	renderToCanvas,
 } from "@/components/public/sprite-font";
 import { ContentCard } from "@/components/public/ui";
-import { FALLBACK_HOTEL_NAME } from "@/lib/brand";
 
 export default function LogoGenerator({
-	initialText = FALLBACK_HOTEL_NAME,
+	initialText = "",
 }: {
 	initialText?: string;
 }) {