logical,txn: detect and replan after destination schema changes

Detect when a running LDR flow has an outdated view of the destination table and replan before applying more rows. Replication should continue if the new schema is compatible; otherwise, the job should surface a schema conflict.

**Out of scope:** Source-side schema changes and enabling `ADD COLUMN`.

**Done when:** A compatible destination schema change causes LDR to replan and continue, while an incompatible change cannot be applied using the stale plan.

**Notes / risk:** The check must protect the write itself and should not trigger replanning for descriptor changes that do not affect replication.

**Depends on:** #173601, #173603

Jira issue: CRDB-66916

Epic CRDB-66920

Start by reading the LDR flow and the prerequisite issues #173601 and #173603, then trace where the destination schema is checked, the plan is selected, and rows are written. Done means a compatible destination change triggers replanning and continued replication, while an incompatible change is rejected without using the stale plan; unrelated descriptor changes must not replan.

Written by the indexing model from the issue text.