Convert mail module to TypeScript with direct method implementation (#1365)

* Initial plan

* Convert all mail module files to TypeScript

Co-authored-by: alexanmtz <88840+alexanmtz@users.noreply.github.com>

* Remove old JavaScript files and fix import issues

Co-authored-by: alexanmtz <88840+alexanmtz@users.noreply.github.com>

* Update mail test to remove canSendEmail stub

Co-authored-by: alexanmtz <88840+alexanmtz@users.noreply.github.com>

* Address code review feedback: restore logging, fix error handling, add notification checks

Co-authored-by: alexanmtz <88840+alexanmtz@users.noreply.github.com>

* Fix payment.support to not check user preferences for admin emails

Co-authored-by: alexanmtz <88840+alexanmtz@users.noreply.github.com>

* Fix TypeScript build errors in mail module

- Fix i18n() calls to use i18n.__() in deadline.ts
- Convert number values to strings for i18n replacements in payment.ts and transfer.ts
- Fix SendGrid content format to use html property in request.ts
- Add null check for sendgrid.apiKey in template.ts
- Fix models.User references to use currentModels in task.ts
- Add @ts-ignore comments for imports without proper type definitions
- Add types: ["node"] to tsconfig.json for Node.js globals
- Restore missing import statements in task.ts

Co-authored-by: alexanmtz <88840+alexanmtz@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: alexanmtz <88840+alexanmtz@users.noreply.github.com>

Author: Copilot