Relax ShareDialog email validation regex

[vibhutomer]

Description

This PR addresses a bug where the ShareDialog email validation strictly rejected valid email addresses containing hyphens or subdomains (e.g., user@my-domain.com or user@mail.university.edu).

Proposed Changes

• Updated the RegExp string in lib/app/utils/share_dialog.dart to appropriately handle - and . characters within the domain grouping.
• Ensured users are no longer blocked from sharing alarms with standard workplace or university email addresses.
• Note: As I lack the local Firebase google-services.json to bypass the Google Auth flow and reach the Share UI manually, I isolated and verified the regex logic locally via a standalone Dart script.

Fixes #924

Screenshots

Checklist

• Tests have been added or updated to cover the changes
• Documentation has been updated to reflect the changes
• Code follows the established coding style guidelines
• All tests are passing