refactor: move retained-parent priority into Pine compatibility

[luisleo526]

Depends on pineforge-4pass/pineforge-codegen-oss#128; merge the codegen bridge first.

A retained child order can carry an older priority than its canceled and recreated parent. The engine currently changes their priority through a default-on Pine rule limited by exact book size, incarnation adjacency, quantity spelling and source context.

Move that complete legacy rule and its metadata interpretation into explicit Pine compatibility. The native comparator consumes an immutable, identity-bound sequence decision after fill phase; native construction and metadata alone do not enable the rule. One explicit Pine attachment selects cap and priority, while existing cap-only APIs stay cap-only. Shared order identities, OCA mutation and financial expectations are preserved.

This transfers one rule out of native decision authority. It does not implement the separate generic child-activation/event-queue machine. Old generated C++ still compiles but must be regenerated to select Pine priority. Internal C++ layout/hash domains advance to v4; public C signatures and PODs are unchanged, and matching headers/library are required. The paired codegen bridge must merge first.

README now records the previously shipped unchanged scoreboard and the documented native exception: actual target net zero plus no individual regression. The formal strict-positive gate is unchanged; actual FAILs remain recorded and promotion defers without PASS.

Validation completed locally: 265 native tests passed / one existing WebSocket skip, 2,814 codegen tests passed / one existing parser skip, independent source review and final exact-commit Grok GREEN (0/0/0). Generated-output fixture changes are limited to a byte-proven constructor block; financial assertions are unchanged. Both fixed-population Cloud runs completed 72/72 cases and all 4,190 probes. Independent raw CSV, count, full-grade, substantive verifier and complete Postgres projection checks show zero differences against the shipped control and official baseline. Both target bands have zero entrants and zero leavers, with no individual regression. No grading metric, reference tape, feed or population was changed.

Part of #227 and #231.

Formal gate executions pineforge-pr-gate-zvv9w and pineforge-pr-gate-frs7d remain FAIL: target.not-positive. The owner authorized native fixes with actual net zero and no individual regression; negative movement is outside that exception. No PASS receipt is claimed and baseline promotion remains deferred.