The README instructs `cp .env.example .env` but no template was committed;
the .gitignore also excluded .env.* which would have hidden it.
- Add .env.example with DB_PASSWORD, SECRET_KEY, JELLYFIN_URL, JELLYFIN_API_KEY
- Add !.env.example exception to .gitignore so the template is tracked
Closes DAP-43.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>