feat(transport): unify directstream and fanout route hints

[marcus-pousette]

Summary

• add shared RouteHint types in stream-interface for directstream ACK route hints and fanout route token hints
• expose route hint accessors from DirectStream routes (best + full list)
• expose fanout route-token hint lookup for topic/root/target
• add getUnifiedRouteHints in pubsub control plane to combine directstream and fanout hints
• add fanout topics test asserting both hint types are available

Validation

• pnpm -C packages/transport/stream-interface run build
• pnpm -C packages/transport/stream run build
• pnpm -C packages/transport/pubsub-interface run build
• pnpm -C packages/transport/pubsub run build
• node ./node_modules/aegir/src/index.js run test --roots ./packages/transport/stream -- -t node --grep "route"
• node ./node_modules/aegir/src/index.js run test --roots ./packages/transport/pubsub -- -t node --grep "unified route hints"

Refs #600