test(calendar): e2e coverage for M2 promote-external flow

[h4yfans]

Summary

Adds end-to-end Playwright coverage for the only M1/M2/M3 user-visible flow that lacked it: clicking an externally-owned Google calendar event and promoting it into a native Memry event.

M1 (correctness fixes) and M3 (etag + field-clock conflict resolution) are entirely internal to the sync layer — their unit suites in `sync-service.test.ts`, `field-merge-calendar.test.ts`, `onboarding.test.ts`, and `promote-external-event.test.ts` already exercise every branch with a mocked `GoogleCalendarClient`. M2's promote flow is the one path that crosses main ↔ renderer ↔ DB and needed regression protection at the Playwright layer.

What changed

• New `apps/desktop/tests/e2e/calendar-promote-external.e2e.ts` — 5 tests, BDD-style `#given/#when/#then` naming, `data-testid`-first selectors:
  1. Click imported chip → promote dialog appears with the M2 copy ("Edit this event in Memry?").
  2. Cancel → dialog closes, no popover, imported chip still present.
  3. Confirm → dialog closes, edit popover opens pre-populated with the external title.
  4. Rename after promote + save → renamed chip appears on the calendar.
  5. `promoteConfirmDismissed=true` in settings → dialog skipped, popover opens directly.
• Replaced the pre-M2 `test.skip` placeholder in `apps/desktop/tests/e2e/calendar-comprehensive.e2e.ts` with a comment pointing to the new file.

Reuses the existing `seedCalendarProjection` test hook — no new test infrastructure.

Test plan

• `pnpm typecheck:node` passes
• `pnpm test` full unit suite: 7005 passed / 1 skipped (unchanged baseline)
• `pnpm test:e2e` filtered to `calendar-promote-external`: 5 passed (30.7s) on first run against the existing M2 implementation
• CI green on full `test:e2e`

Notes for reviewer

• All five tests passed on the very first run — no implementation changes were needed, so this is pure regression protection for M2's user-visible contract.
• The new file doesn't duplicate unit coverage: `promote-external-event.test.ts` already asserts row shape, binding ownership mode, mirror archival, and idempotency. The E2E asserts the user-visible flow (dialog copy, click wiring, popover population, persistence to the calendar view).