chore: rebrand to Thoosie Calendar, add favicon

- Rename app title and header from "Six Flags Calendar" to "Thoosie Calendar"
- Update layout metadata title and description
- Update README title
- Add app/icon.svg favicon: amber T on dark background, picked up
  automatically by Next.js App Router

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

app/layout.tsx

@@ -2,8 +2,8 @@ import type { Metadata } from "next";
 import "./globals.css";
 
 export const metadata: Metadata = {
-  title: "Six Flags Calendar",
-  description: "Theme park operating calendars at a glance",
+  title: "Thoosie Calendar",
+  description: "Theme park operating hours and live ride status at a glance",
 };
 
 export default function RootLayout({ children }: { children: React.ReactNode }) {