feat: import and export tickets as CSV

Every ticket of a project can be downloaded as CSV, and a CSV exported
from TaskStream or from Jira can be imported: types, statuses, priorities
and people are matched by id or name, the rest falls back with a warning,
and parents are rebuilt. The settings page previews an import before it
creates anything.

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

libs/api/tracker/application/src/lib/transfer.service.ts

@@ -0,0 +1,31 @@
+import { Injectable } from '@nestjs/common';
+import { CommandBus, QueryBus } from '@nestjs/cqrs';
+import {
+  ExportIssuesQuery,
+  ImportIssuesCommand,
+  ImportReport,
+} from './transfer/import-export';
+
+/** Tickets in and out as CSV (TaskStream's own, or a Jira export). */
+@Injectable()
+export class TransferService {
+  constructor(
+    private readonly commandBus: CommandBus,
+    private readonly queryBus: QueryBus,
+  ) {}
+
+  exportCsv(viewerId: string | null, projectId: string): Promise<string> {
+    return this.queryBus.execute(new ExportIssuesQuery(viewerId, projectId));
+  }
+
+  importCsv(
+    actorId: string,
+    projectId: string,
+    csv: string,
+    dryRun: boolean,
+  ): Promise<ImportReport> {
+    return this.commandBus.execute(
+      new ImportIssuesCommand(actorId, projectId, csv, dryRun),
+    );
+  }
+}