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/api/tracker/application/src/lib/event-handlers/activity-summary.ts

@@ -79,6 +79,7 @@ const ROLE: Record<ProjectRole, string> = {
   [ProjectRole.ADMIN]: 'admin',
   [ProjectRole.MEMBER]: 'miembro',
   [ProjectRole.VIEWER]: 'lector',
+  [ProjectRole.GUEST]: 'invitado',
 };
 
 const FIELD: Record<string, string> = {