Add tx-ordering pre-push checklist to POST-PUSH-PROTOCOL.md

Add tx-ordering checklist subsection to ~/shared-knowledge/POST-PUSH-PROTOCOL.md Phase 1, mirroring the structure of the blast-radius check shipped 2026-06-16. CARRY-FORWARD from 2026-06-17 reflection. PR #12309 BOLT-1286 took 4 substantive cursor-bugbot rounds (each finding the NEXT transaction-ordering or atomicity concern: sanitize-dates → audit-log-out-of-tx → audit-log-back-in-tx → advisory-lock-ordering-before-audit). Same scoping-failure shape as PR #12182 rename. Pattern owed structural enforcement. Rule: when a PR diff touches a Prisma $transaction block, the pre-push checklist enumerates (a) every write inside the tx, (b) every advisory lock, (c) every audit/log row, and verifies the order is `acquire lock → mutate → audit` BEFORE pushing. Implementation: 1. Add Tx-ordering check subsection to POST-PUSH-PROTOCOL.md Phase 1 right after the blast-radius check. 2. Cite PR #12309 BOLT-1286 (2026-06-16) as the originating incident and rule birth. 3. Include a one-line check: grep for $transaction or interactiveTransaction in the diff. If found, run the enumeration before push. 4. Acceptance: next tx-touching PR is the first enforcement. Reference: LEARNINGS 2026-06-17 tx-ordering pre-push checklist rule.