a212e145ac
Adds a dashboard event-visibility tag to ApiKeyConstraints, riding in the existing constraints JSON blob so no auth-store schema migration is needed (design docs/plans/2026-07-10-dashboard-session-acl-tst15.md sections 3/3.1, open call settled per its own recommendation). The tag is visibility-only: no read, write, browse, or subscribe path consults it, and HasRead/HasWriteConstraints ignore it. GatewaySession gains an immutable, ordinal-ignore-case Tags set stamped at construction from the owning API key, forwarded by MxAccessGatewayService.OpenSession from the resolved ApiKeyIdentity — never from the wire request, so a client cannot label its own session with another tenant's tag. ISessionManager gains a tag-carrying OpenSessionAsync overload whose default implementation forwards to the tagless one, so an implementation that does not model tags opens an untagged (least visible) session. apikey create-key gains --dashboard-tags team-a,team-b (repeatable, trimmed, de-duplicated; an empty segment is rejected rather than dropped) and list-keys prints the tags column. No enforcement yet — the EventsHub ACL that consumes the tag is a later change.