Rename the app from scopa to tavolo

The platform now hosts multiple card games, with scopone scientifico as
the first one. Rename the brand wherever it is not a game rule:

- move the Python package to server/src/tavolo and update imports
- rename the Postgres database/user, OIDC issuer path, client id and
  Redis key prefixes to tavolo (clean break: existing pgdata volumes and
  live games are not migrated)
- rename the Cargo package to tavolo-web and set the page title to Tavolo
- update docs and the Docker image path to woggioni/tavolo

The scopa game term (clearing the table) in the engine, state and web UI
is intentionally left untouched.

web/src/api.rs

@@ -1,4 +1,4 @@
-//! REST client for the scopa backend. Same-origin requests carry the
+//! REST client for the tavolo backend. Same-origin requests carry the
 //! session cookie automatically.
 use crate::model::*;
 use gloo_net::http::Request;