Expand unit test coverage for the deal-stats data layer + B24 SDK smoke test

[IgorShevchik]

Context

PR #3 introduced the first unit tests (test/formatters.test.ts, test/helpers.test.ts, test/utils.test.ts) covering pure helpers. Several higher-value modules remain at 0% coverage, and the @bitrix24/b24jssdk 1→2 major bump is not exercised by any test. This issue tracks closing those gaps as a dedicated follow-up (kept out of PR #3 to avoid bloating a dependency-update PR and because it needs additional test harness setup).

Coverage gaps to close

• app/composables/useDealStats/api.ts — the core CRM integration (currently untested):
  • paginated loading via b24.actions.v2.fetchList.make (mock the async generator with canned pages);
  • date-range boundary normalization (setHours(0,0,0,0) / 23:59:59.999);
  • the stageSemanticId === 'P' ? null : ... closedate nulling — this is the exact invariant getLatestSales's filter relies on, currently only assumed via hand-built fixtures;
  • revenue aggregation per currency, successfulDeals count, and uniqueCustomers dedup (contactId / companyId / 'empty' fallback).
• app/composables/useDealStats/index.ts — orchestration: processCrmData / loadDeals, mock-vs-B24 branching, partial-stat callback merging, variation calc (current vs previous period), currency-list cleanup, and the SdkError error/toast path. Needs Nuxt auto-import mocking (useI18n, useToast, shallowRef, …) or @nuxt/test-utils.
• app/composables/useDealStats/formatters.ts — formatDateRange and formatDateTimeShort are untested (add cases under the pinned TZ=UTC).
• app/composables/useDealStats/helpers.ts — groupSalesByDate has two live @todo fix this markers; add edge cases (closedate before the earliest timestamp, duplicate/near timestamps, unsorted input) that pin current behavior before any fix.
• app/composables/useDealStats/mocks.ts — smoke tests for generateMockStats / generateMockChart / generateMockSales (e.g. count, chart length matches dates).

B24 SDK smoke test (major bump 1→2)

No test currently exercises the SDK integration surface (useB24 init/set/get, initializeB24Frame, useB24Helper, LoadDataType, actions.v2.fetchList). Add at least a mocked smoke test that pins the expected shapes so a future SDK bump that changes them is caught by CI.

Test-harness prerequisites

• vitest.config.ts currently has no setupFiles / path aliases / coverage config. Composable/orchestration tests will need Nuxt auto-import mocking (or @nuxt/test-utils) and possibly ~/#imports aliases.
• Consider wiring vitest run --coverage and a coverage threshold into CI (.github/workflows/ci.yml) so gaps stay visible.

Acceptance

• api.ts covered (pagination, date bounds, closedate nulling, aggregation, dedup)
• index.ts orchestration covered (mock + B24 branches, error path)
• formatDateRange / formatDateTimeShort covered (TZ-pinned)
• groupSalesByDate edge cases covered
• mocks.ts smoke-tested
• B24 SDK smoke test in place
• coverage reporting wired into CI

Follow-up to PR #3.