fix(core): reconcile order line refunded quantity

[tazzytazzy]

Summary

Fixes #2709.

Adds a guarded core migration to reconcile
order_lines.refunded_quantity on existing Lunar 2.x databases.

The line-item refund work added this column to the order-lines create-table
baseline. Databases that had already recorded that migration did not rerun it,
so they could receive refund_lines while still lacking the rollup column.

When those databases processed a line-item refund, Lunar could complete the
payment driver's refund call and then fail while persisting the line allocation
because RefundOrder increments the missing column.

Changes

• adds a prefix-aware reconciliation migration after refund_lines;
• safely no-ops when the table is absent or the column already exists;
• adds an unsigned refunded_quantity column with a default of 0;
• preserves existing order-line records;
• uses a non-destructive rollback because the flat baseline owns the column.

Tests

• verifies the column is added and existing rows default to zero;
• verifies repeated execution is safe;
• verifies already-current and missing-table schemas are no-ops;
• verifies core migrations still roll back and re-apply;
• verifies existing line-item refund behavior remains green.

Scope

This PR is limited to Lunar's provider-independent schema reconciliation. It
does not change provider behavior, refund transaction boundaries, ledger
attribution, replay semantics, RefundRequest, or historical allocation data.