Improve WellAI email templates and links

[Sarasaidin]

Summary

• Update the password reset email with a professional WellAI-branded HTML template.
• Update the patient access request email with a professional WellAI-branded HTML template.
• Replace hardcoded email links with the configurable FRONTEND_URL.
• Add the WellAI logo to both emails using an inline CID image.
• Keep the existing email expiry and security information.

Testing

• Python syntax check passed for both modified routers.
• git diff --check passed.
• Verified /reset-password/:token frontend route exists.
• Verified /accept-access-request/:token frontend route exists.