fix: skip Matomo tracking on localhost

[marc0olo]

Summary

• Moves the Matomo tracking script from an inline blob in `astro.config.mjs` to a dedicated `public/matomo.js` file
• Adds a `location.hostname` guard so tracking is skipped on `localhost` and `127.0.0.1` — covers both `npm run dev` and `npm run preview`

Sync recommendation

hand-written