feat(mst2): persist publication request receipts

[Ivanbeethoven]

Persist MST/2 publication request identity and durable receipts for the existing trunk queue adapter. A versioned digest binds the persisted queue request; replay and conflict checks run under the namespace/root CAS transaction. Successful no-op operations receive durable receipts without advancing the publication sequence or creating an outbox entry. Legacy receipts preserve their data and fail closed when their identity cannot be established.

The migration regression locates the request-digest migration by name and reruns that exact migration inside a transaction. The current config base is synchronized through a normal merge, preserving the digest and retention migrations and all six migration-order tail entries. Strict-request fixtures explicitly require successful runtime registration before inspecting the returned context.

Validation: complete Linux repository gates passed on 27eae59431a88b168f28ed4bff2c280d2d0760f0 (run 37349534877). Nightly formatting, strict all-target/all-feature Clippy, both builds, real isolated PostgreSQL/Redis/RustFS dependencies, cargo test --all, and dependency cleanup all succeeded. All 18 targets completed: 2,222 passed, zero failed, and two pre-existing ignored tests; the library had 2,001 passing tests. Source-selected request, publication, retention, scope, alias-migration, and real Push receipt/no-op regressions also passed. Two independent source reviews, clean local state, and matching local/remote/PR commit identities were verified.

This PR covers the existing trunk queue adapter. Full all-writer namespace publication remains separate work. No benchmark, deployment, or physical GC result is claimed.