Add Config.ProjectCode + Config.SeedFromUpstream so multiple hubs sharing a project-code propagate commits over a single .sync subject. Adds an auto-publish notification on a sibling .commit subject + pull-on-notify subscriber, closing the cross-process Fossil sharing gap from #156.

- hub/nats_transport.go: libfossil.Transport over nats request/reply - hub/clone.go: HTTP-based SeedFromUpstream helper (NATS-clone deferred) - hub/repo.go: Repo.publish hook fired after successful Commit - hub/hub.go: startCommitSubscriber + Config plumbing + NoEcho - hub/cross_leaf_test.go: gold-path propagation, subject alignment, drift guard - libfossil pin -> v0.6.1 (CreateOpts.ProjectCode)

Design: docs/superpowers/specs/2026-05-12-cross-leaf-fossil-sync-design.md Protocol: docs/architecture/sync-protocol.md ("NATS-Wrapped Sync")

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com> check-in: 6f9e3e40d0 user: [email protected] tags: trunk