feat: pinned tickets, at hand on the home page and in search

Each person pins up to 20 tickets from the ticket's page («Fijar»). They
show as a strip under the projects on the home page and in the search
palette before typing. Private and without history, like the views of
«my work» (Mongo `pinned_issues`); tickets in the trash or out of reach
are left out, and when the list is full the unreadable ones are dropped
first.

API: GET /api/me/pins, PUT/DELETE /api/issues/{issue}/pin; GraphQL
myPins, pinIssue, unpinIssue and Issue.pinned.

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

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

@@ -190,6 +190,8 @@ export interface Issue extends IssueSummary {
   attachments: Attachment[];
   /** People following the ticket. */
   watchers: UserRef[];
+  /** Whether I keep it pinned (home page and search). */
+  pinned: boolean;
   checklist: ChecklistItem[];
   /** Commits, branches and pull requests that mention it. */
   devLinks: DevLink[];