[ZhuchkaTriplesix]

Summary

With an empty name and a URI, PostgreSQL named the connection after the URI's host, MySQL MySQL (URI), and Redis and MongoDB after the form's host field (Redis localhost:6379), so several URI connections looked identical in the sidebar.

defaultConnectionName (features/connections/connection_default_name.dart) is now used by all four forms:

• <Type>: host:port from the URI; the port is the URI's, else the type's default; a +srv URI has none (MongoDB: c0.example.net);
• <Type> (URI) when the URI has no host or does not parse;
• without a URI, the name from the fields, as before.

An explicitly typed name always wins. The PostgreSQL name is unchanged.

Tests: the helper (URI with and without port, +srv, no host, no URI) and the e2e form scenarios assert the saved name contains the URI's host.

Closes #1257

Test plan

• CI: all test sections pass (no local runs, per team rule)