Security hardening: drop npm deps and self-host Outfit font

- Remove package.json / package-lock.json. The only dependency was
  claude-flow (dev tooling, never loaded by the game), which pulled in
  49 known vulnerabilities (2 critical, 28 high) and could be installed
  by the Cloudflare Pages build.
- Self-host the Outfit variable font (latin + latin-ext woff2, SIL OFL)
  in fonts/ instead of loading it from Google Fonts. This removes the
  last third-party origins from the CSP (style-src / font-src are now
  'self' only), stops sending visitor IPs to Google, and makes the font
  work offline.
- Precache the font files in the service worker and bump CACHE_NAME to
  tortugotchi-v18.

_headers

@@ -1,5 +1,5 @@
 /*
-  Content-Security-Policy: default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; font-src 'self' https://fonts.gstatic.com; img-src 'self' data:; connect-src 'self'; manifest-src 'self'; worker-src 'self'; frame-ancestors 'none'; base-uri 'self'; form-action 'self'; object-src 'none'; upgrade-insecure-requests
+  Content-Security-Policy: default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; font-src 'self'; img-src 'self' data:; connect-src 'self'; manifest-src 'self'; worker-src 'self'; frame-ancestors 'none'; base-uri 'self'; form-action 'self'; object-src 'none'; upgrade-insecure-requests
   X-Frame-Options: DENY
   X-Content-Type-Options: nosniff
   Referrer-Policy: no-referrer