fix: preserve media metadata in SQL exports

[ShiroKSH]

Summary

• Preserve media_id and required Gym visual attribution in every generated SQL schema and INSERT statement.
• Apply the fix to both shipped SQL exporters: the standalone setup guide and the embedded browser exporter.
• Include both fields in the generated backend prompt's dataset contract.

Root cause

The exporters created and populated only 20 columns despite each dataset record carrying media_id and attribution. Generated imports silently discarded the original media reference and required credit.

Checks

• Generated and inspected DDL/INSERT output for MSSQL, PostgreSQL, MySQL, and SQLite in both exporters.
• Imported all 1,324 records into SQLite from each exporter; media_id and attribution were populated for every row.