Import #4 : from DB connection

**Goal** : use a DBI connection to import a table

Features:
* Use existing DBI connection from Global Env ?
* Interface to connect to a DB with `DBI::dbConnect` ?
* Get schemas and tables in DB and let the user choose

Begin by locating the existing import flow and Global Env handling, then review the DBI::dbConnect entry point and how schemas and tables can be enumerated. Clarify whether to reuse an existing DBI connection or expose a connection interface, and define the table-selection behavior as done; no file or test is named in the issue.

Written by the indexing model from the issue text.