MYSQL-OBJ-003: Visible and invisible column management

Fixture

• init.sql creates obj003_column_test with id, name, secret, and created_at columns.
• On MySQL 8.0.23+, secret is made INVISIBLE via ALTER TABLE ... MODIFY COLUMN ... INVISIBLE.
• grants.sql grants SELECT, INSERT, UPDATE, ALTER to the test user.
• cleanup.sql drops the test table.

Verification

1. Connect with the test user.
2. Open the table in the table editor.
3. Verify the column list shows VISIBLE/INVISIBLE for each column.
4. The secret column should show INVISIBLE.
5. Toggle secret from INVISIBLE to VISIBLE and preview the SQL.
6. Execute and refresh — the column should show VISIBLE.
7. Create a new invisible column and verify the SQL includes INVISIBLE.
8. Verify SELECT * omits invisible columns (explained in UI tooltip).
9. Explicitly querying an invisible column by name still works.
10. On MySQL 5.7 and 8.0.22 or earlier, the visibility control should not appear.