bug(connections): URI-only PostgreSQL connections lose host/port display metadata

[ZhuchkaTriplesix]

postgresql_connection_form.dart sets host and port to null when a URI is provided, and generates a generic name 'PostgreSQL (URI)'. The sidebar subtitle is hidden.

Impact: Users cannot quickly identify which URI connection is which in the connection tree.

Expected: Extract host and port from the URI for display, and derive a readable name from them.

Acceptance criteria:

• Parse host and port from the URI for display purposes.
• Use a name like PostgreSQL: <host> when no custom name is entered.
• Update form tests.