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/mobile-nav.tsx

@@ -3,7 +3,6 @@
 import { AnimatePresence, motion } from "motion/react";
 import Image from "next/image";
 import { type ReactNode, useRef, useState } from "react";
-import { FALLBACK_HOTEL_NAME } from "@/lib/brand";
 import { mobileMenuVariants } from "@/lib/motion";
 
 interface MobileNavProps {
@@ -17,7 +16,7 @@ export function MobileNav({
 	children,
 	menuLabel = "Open menu",
 	closeLabel = "Close menu",
-	brandLabel = FALLBACK_HOTEL_NAME,
+	brandLabel = "",
 }: MobileNavProps) {
 	const [open, setOpen] = useState(false);
 	const detailsRef = useRef<HTMLDivElement>(null);

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;
 }) {