feat: guest role for clients and outsiders

A project member can be a GUEST. In a private project a guest only sees
the tickets they take part in (opened, assigned or followed): every other
ticket answers 404, also in my work, realtime changes, blockers and
linked tickets, and project-wide views (activity, statistics, dashboard,
releases, sprints, epics, trash) answer 403. Guests open tickets without
assigning or planning them, and comment, attach, follow and vote on their
own; they change nothing else. In a public project they see what anyone
does. The web gives them only Tablero, Lista and Miembros and loads none
of the project-wide data.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/web/tracker/domain/src/lib/models/enums.ts

@@ -41,6 +41,8 @@ export enum ProjectRole {
   ADMIN = 'ADMIN',
   MEMBER = 'MEMBER',
   VIEWER = 'VIEWER',
+  /** From outside (a client): only the tickets they take part in. */
+  GUEST = 'GUEST',
 }
 
 export enum ReleaseStatus {