OG cards, deploy scripts, OAuth scaffolding ...

- backend/og.py: 1200x630 PNG result cards (Pillow, brutalist dark theme, cached per result_id)
- main.py: server-rendered /result/<id> and /v/<id> with dynamic OG meta injection (fixes missing /result route), /og/<id>.png card endpoint
- backend/oauth.py: X OAuth2 PKCE + Instagram FB-Login scaffolding, 503 until apps registered; /auth/x/* and /auth/ig/* routes wired
- scripts/deploy.sh: systemd unit + nginx + certbot, idempotent
- .env.example: all runtime + OAuth config vars
- live-tested: OG meta injection, PNG generation, 404s, OAuth 503 stubs