docs: Zenoh connector and ROS 2 for the native release (design 053 s16)

[lxsaah]

Stage s16 of docs/design/053-implementation-plan.md: the docs for the native release. The embedded backend (s13–s15) is deferred until zenoh-nostd is on crates.io.

What changes

CHANGELOGs, written at wrap-up time:

• CHANGELOG.md: a global "Added — Zenoh connector and ROS 2 topics" entry, and links to the two new crate CHANGELOGs.
• aimdb-core: the existing RouteInfo and InboundDispatch bullets gain type_id and routes() / InboundRouteInfo; a new bullet covers WIRE_FORMAT_KEY and the setters that clear it.
• aimdb-data-contracts: WireFormat and the two WIRE_FORMAT constants; the ros2 feature (RosMessage, the ros2:: checks, the derive re-export); the linkable-cdr feature (link_codecs::Cdr<N>).
• aimdb-derive: #[derive(RosMessage)], and #[derive(Linkable)] now setting WIRE_FORMAT = Json.
• New aimdb-cdr/CHANGELOG.md and aimdb-zenoh-connector/CHANGELOG.md.

User docs:

• aimdb-zenoh-connector/README.md: installation and a features table; quick starts for ROS 2 topics, plain Zenoh and the shared gateway session; QoS overrides and refusals; limits (reliability only advertised; no services, actions or TRANSIENT_LOCAL; compression stays off, with RUSTSEC-2026-0041); testing. Links are absolute GitHub URLs, so they work on crates.io.
• New docs/aimdb-and-ros2.md: the ROS side's setup, message types and where the hash comes from, the field mapping table, domain and namespace, links and QoS, what fails the build, the microcontroller gateway, checking from the ROS 2 CLI, and what isn't there yet.
• docs/aimdb-usage-guide.md: a "Zenoh Connector and ROS 2" section and a "Ready for Use" line. "All connectors support both Tokio and Embassy" is corrected, since Zenoh is std only for now.
• README.md: Zenoh and ROS 2 added to the connector list.
• The crate docs (lib.rs) and Cargo.toml now describe embedded as reserved for the zenoh-nostd backend, rather than claiming a backend that doesn't exist yet.

Release readiness:

• aimdb-zenoh-connector drops publish = false and joins PUBLISH_ORDER after aimdb-mqtt-connector, so the next make publish releases it.
• Locally, phase 1 of publish-check (packaging the whole publish set with --no-verify) succeeds, including the new crate with its aimdb-data-contracts ros2 dependency. Phase 2, which builds every crate, isn't run in CI or here.

Plan (053-implementation-plan.md):

• s13–s15 are marked deferred: a git dependency on zenoh-nostd would make the crate unpublishable, native backend included.
• s16's scope is now the native release.
• New follow-ups, outside the plan's stages: refresh design 012, the connector development guide, which still describes the pre-054 Connector trait and pumps; a BYOC tutorial built on this connector; the manufacturing-cell demo.

After this

Once s12 (#314) and this PR are merged, feat/aimdb-zenoh-connector is ready to merge into main with the native backend.

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