rename project from SixFlagsSuperCalendar to Thoosie Calendar

Update package names, Docker image tags, CI/CD workflow, and
documentation to reflect the public brand name. References to
the actual Six Flags theme park chain/API are intentionally kept.

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

backend/package.json

@@ -1,5 +1,5 @@
 {
-  "name": "sixflags-backend",
+  "name": "thoosie-backend",
   "version": "0.1.0",
   "private": true,
   "scripts": {