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/api/tracker/domain/src/lib/read-models/saved-filter.read-model.ts

@@ -56,3 +56,10 @@ export class MyViewReadModel {
   criteria!: MyViewCriteriaReadModel;
   createdAt!: string;
 }
+
+/** A ticket someone keeps at hand: private to them, no history. */
+export class PinnedIssueReadModel {
+  ownerId!: string;
+  issueId!: string;
+  pinnedAt!: string;
+}