fix(admin): qualify ambiguous column name in marketplace_activity query

`credit_ledger cl` joined with `suppliers s` — both have `id`, so
SQLite raised OperationalError. Qualify as `cl.id` and `cl.supplier_id`.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/src/padelnomics/admin/routes.py

@@ -881,7 +881,7 @@ async def marketplace_activity():
            FROM lead_forwards lf
            JOIN suppliers s ON s.id = lf.supplier_id
            UNION ALL
-           SELECT 'credit' as event_type, id as ref_id, supplier_id as ref2_id,
+           SELECT 'credit' as event_type, cl.id as ref_id, cl.supplier_id as ref2_id,
                s.name as actor, cl.event_type as detail,
                CAST(cl.delta AS TEXT) as extra, cl.created_at
            FROM credit_ledger cl