Menu Bar: Implement Connection -> Connect, Disconnect, Disconnect All

[ZhuchkaTriplesix]

The connection session controls (Connect, Disconnect, Disconnect All, Disconnect Others) are currently stubs. The Connect button is disabled.

Proposed Solution:

• Connect: Connect the highlighted database connection.
• Disconnect: Release the lease (PgLease.release(), SqliteLease.release(), etc.) for the current active workspace database.
• Disconnect All: Iterate over connection services and close all open database connections.