Names the router's twins for RT13 and RT18

[johnnyt]

What

docs/publish-time-checks.md still read RT18's twin as NONE and said RT13's dropped: unmatched_event outcome was deferred. statifier_router 0.5.0, published on Hex, ships both, so the two router rows now name the router surface and the version.

• RT18 (a delayed send of the router's type with no timer queue): the twin is StatifierRouter.Contracts.check/3 (statifier_router 0.5.0), which lists the send under unregistered_routes with reason :no_timer_queue.
• RT13 (an event the receiving chart never listens for): through a binding, StatifierRouter.route/3 answers {:dropped, binding_id, :unmatched_event} and the binding's ledger row reads dropped: unmatched_event (statifier_router 0.5.0); the execution still took the event, and a send to the execution target keeps its outcomes.

No changelog fragment: documentation only (changelog.d/README.md).

Provenance

RT13's twin cell also read StatifierRouter.Contracts.check/3 as "statifier_router main, next release". The page's own rule is that a twin moving from a main branch to a release changes its row, and check/3 first shipped in statifier_router 0.3.0, so this row's twin now names 0.3.0. The same stale wording in the twin cells of RT1, RT2 and RT3 is left for a separate change.

Checks

• Docs only: no Elixir code changes, so the repo's commit rule runs no gate. mix quality --profile merge ran green on this branch; its ADR judge stage skipped, since no file in the diff is in a judged scope. The final rebase onto main changed nothing in this diff.
• Claims read against statifier_router at the v0.5.0 tag: its CHANGELOG's 0.5.0 section; StatifierRouter.Contracts's route_reason type and check/3, which emit a :no_timer_queue entry under :unregistered_routes; StatifierRouter.Delivery's taken clause, which records dropped: unmatched_event for a binding whose step selected no transition and leaves the execution target's outcomes alone. StatifierRouter.Contracts is absent at the v0.2.0 tag and present at v0.3.0, whose CHANGELOG section introduces check/3.
• Review: own pre-request review of the diff; no record under docs/adr/ is touched.