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.

sw.js

@@ -1,4 +1,4 @@
-const CACHE_NAME = 'tortugotchi-v17';
+const CACHE_NAME = 'tortugotchi-v18';
 const ASSETS = [
   './',
   './index.html',
@@ -7,6 +7,8 @@ const ASSETS = [
   './manifest.json',
   './icon-192.png',
   './icon-512.png',
+  './fonts/outfit-latin.woff2',
+  './fonts/outfit-latin-ext.woff2',
   './media/turtvox001_another_day_in_the_deep_blue.m4a',
   './media/turtvox002_best_human_ever.m4a',
   './media/turtvox003_bitten_shell_but_ok.m4a',