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/application/src/lib/pins.service.ts

@@ -0,0 +1,31 @@
+import { CommandRunner } from '@task-stream/api/shared/application';
+import { Injectable } from '@nestjs/common';
+import { QueryBus } from '@nestjs/cqrs';
+import { IssueReadModel } from '@task-stream/api/tracker/domain';
+import {
+  GetMyPinsQuery,
+  IsIssuePinnedQuery,
+  PinIssueCommand,
+} from './saved-filters/pins';
+
+/** Pinned tickets: the few someone keeps at hand, across projects. */
+@Injectable()
+export class PinsService {
+  constructor(
+    private readonly commands: CommandRunner,
+    private readonly queryBus: QueryBus,
+  ) {}
+
+  /** Mine, most recently pinned first. */
+  mine(ownerId: string): Promise<IssueReadModel[]> {
+    return this.queryBus.execute(new GetMyPinsQuery(ownerId));
+  }
+
+  isPinned(ownerId: string, issueId: string): Promise<boolean> {
+    return this.queryBus.execute(new IsIssuePinnedQuery(ownerId, issueId));
+  }
+
+  pin(ownerId: string, issueId: string, pinned: boolean): Promise<void> {
+    return this.commands.execute(new PinIssueCommand(ownerId, issueId, pinned));
+  }
+}