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/queries/search-issues.query-handler.ts

@@ -20,6 +20,11 @@ export class SearchIssuesQueryHandler
     if (watching && !query.viewerId) return { items: [], total: 0 };
     return this.findIssues.search({
       ...filter,
+      participantId:
+        (await this.access.participantScope(
+          query.filter.projectId,
+          query.viewerId,
+        )) ?? undefined,
       watcherId: watching ? (query.viewerId ?? undefined) : undefined,
       limit: Math.min(query.filter.limit, 200),
     });