Add .env.example and remove committed secrets

[KniggeMS]

Create a .env.example with placeholder env vars (VITE_SUPABASE_URL, VITE_SUPABASE_ANON_KEY, VITE_TMDB_API_KEY, VITE_OMDB_API_KEY). Ensure .env is in .gitignore and rotate any exposed keys found in working directory.

[KniggeMS]

.env.example wurde in commit 2bbcc54 hinzugef├╝gt.