Add issue change history and daily issue stats

Issue changes are recorded per field in the issue_change table, in the same
transaction as the issue itself. The new history module exposes:
- GET /api/issues/:issueId/history — change timeline grouped by save
- GET /api/issues/stats/daily — created, status transitions and status
  snapshot per day, with time zone support

The migration backfills history for existing issues. Setting a field to its
current value no longer bumps updatedAt or emits issue.updated.

src/modules/history/application/dto/issue-history.dto.ts

@@ -0,0 +1,21 @@
+import type { IssueChangeField } from '../../../issue/domain/entities/issue-change.js';
+import { UserDto } from '../../../user/application/dto/user.dto.js';
+
+export class IssueFieldChangeDto {
+  field: IssueChangeField;
+  oldValue: string | null;
+  newValue: string | null;
+  /** Только для field = assignee: пользователи из oldValue/newValue (null — не назначен или удалён) */
+  oldUser?: UserDto | null;
+  newUser?: UserDto | null;
+}
+
+/** Одно сохранение задачи: кто, когда и какие поля изменил */
+export class IssueHistoryEntryDto {
+  /** changeId */
+  id: string;
+  changedAt: Date;
+  actorId: string | null;
+  actor: UserDto | null;
+  changes: IssueFieldChangeDto[];
+}