Upgrade cypress-mailpit 0.0.4 → 2.0.0

# Upgrade cypress-mailpit 0.0.4 → 2.0.0 (major)

Dependabot PR #7499. Dev dependency (`^0.0.4`, resolved 0.0.4) — Cypress email-testing plugin, imported in `test/e2e/frontend/cypress/support/commands.js`. Pulled out of the weekly Dependabot slot per the major-version process — needs an owner and verification, not a batch merge.

## Compatibility pre-check

- ✅ Peer `cypress >=15.10.0`; installed is 15.18.1.
- ✅ No `engines` constraint published for 2.0.0.
- ✅ No direct `cy.mailpit*` / `getMailpit` command usage found in specs; only the plugin import in `commands.js`. Mailpit itself is run via Docker in `test/e2e/frontend/environments/smtp.js`.
- ✅ No `MAILPIT_URL` configured in the repo (plugin default), so the config-key migration below has nothing to port.

## Breaking changes to review

- 0.x → 2.0 crosses to a stable major; treat all API as potentially changed.
- Mailpit URL config moved from `Cypress.env()` to `Cypress.expose()` (`MAILPIT_URL`) — README.
- Minimum Cypress bumped to `>=15.10.0` — README.
- Full renamed/removed command list not enumerated in release notes: to confirm from changelog.

## To do before merge

- [ ] Run the e2e specs that use mailpit; reconcile any renamed commands.
- [ ] Read the 2.x changelog / README.

## Refs

- Branch: `dependabot/npm_and_yarn/cypress-mailpit-2.0.0`
- PR: #7499
- Upstream: https://github.com/pushpak1300/cypress-mailpit

Start by reading the cypress-mailpit 2.x changelog and README, then inspect its import in test/e2e/frontend/cypress/support/commands.js and the Mailpit environment in test/e2e/frontend/environments/smtp.js. Run the e2e specs that use Mailpit and verify that the plugin import, any commands, and configuration remain compatible with Cypress 15.18.1.

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