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/use-cases/get-daily-issue-stats/get-daily-issue-stats.use-case.ts

@@ -0,0 +1,73 @@
+import { Inject, Injectable } from '@nestjs/common';
+import { ISSUE_STATUSES, type IssueStatusValue } from '../../../../issue/domain/value-objects/issue-status.vo.js';
+import {
+  ISSUE_HISTORY_REPOSITORY,
+  type IIssueHistoryRepository,
+} from '../../../domain/repositories/issue-history.repository.interface.js';
+import { StatsPeriod } from '../../../domain/value-objects/stats-period.vo.js';
+import { DailyIssueStatsDayDto, DailyIssueStatsDto, IssueStatusCounts } from '../../dto/daily-issue-stats.dto.js';
+import { GetDailyIssueStatsQuery } from './get-daily-issue-stats.query.js';
+
+/**
+ * Статистика задач по дням, считается по истории изменений (issue_change).
+ * Видимость — как у списка задач: только задачи, где пользователь reporter/assignee.
+ */
+@Injectable()
+export class GetDailyIssueStatsUseCase {
+  constructor(
+    @Inject(ISSUE_HISTORY_REPOSITORY)
+    private readonly historyRepository: IIssueHistoryRepository,
+  ) {}
+
+  async execute(query: GetDailyIssueStatsQuery): Promise<DailyIssueStatsDto> {
+    const period = StatsPeriod.create({ from: query.from, to: query.to, timeZone: query.timeZone });
+    const range = {
+      userId: query.userId,
+      projectId: query.projectId,
+      from: period.from,
+      to: period.to,
+      timeZone: period.timeZone,
+    };
+
+    const [events, statuses] = await Promise.all([
+      this.historyRepository.countDailyEvents(range),
+      this.historyRepository.countDailyStatuses(range),
+    ]);
+
+    // Каждый день периода попадает в ответ, даже если в нём ничего не было
+    const days = new Map<string, DailyIssueStatsDayDto>(
+      period.days.map((date) => [
+        date,
+        { date, created: 0, transitions: emptyStatusCounts(), byStatus: emptyStatusCounts() },
+      ]),
+    );
+
+    for (const event of events) {
+      const day = days.get(event.date);
+      if (!day) continue;
+
+      if (event.kind === 'created') {
+        day.created += event.count;
+      } else if (isKnownStatus(event.status)) {
+        day.transitions[event.status] += event.count;
+      }
+    }
+
+    for (const entry of statuses) {
+      const day = days.get(entry.date);
+      if (day && isKnownStatus(entry.status)) {
+        day.byStatus[entry.status] += entry.count;
+      }
+    }
+
+    return { from: period.from, to: period.to, timeZone: period.timeZone, days: [...days.values()] };
+  }
+}
+
+function emptyStatusCounts(): IssueStatusCounts {
+  return Object.fromEntries(ISSUE_STATUSES.map((status) => [status.alias, 0])) as IssueStatusCounts;
+}
+
+function isKnownStatus(status: string): status is IssueStatusValue {
+  return ISSUE_STATUSES.some((known) => known.alias === status);
+}