Feature/ics rework/mime

[lucs7]

This pull request enhances the email attachment handling system by allowing MIME types to be specified for string attachments, ensuring correct content types are used when sending emails.

Depends on #1656

[Copilot]

Pull request overview

This PR extends LibreBooking’s email attachment pipeline so IEmailMessage string attachments can optionally provide an explicit MIME Content-Type, allowing reservation .ics attachments to be sent with text/calendar; ...; method=REQUEST instead of relying on filename-based detection. It also incorporates the attachment-leak fix from the dependent PR (#1656) by clearing PHPMailer attachments before each send.

Changes:

• Add optional $mimeType support to IEmailMessage::AddStringAttachment(...) and propagate it through EmailMessage + EmailService into PHPMailer’s addStringAttachment(...).
• Update reservation ICS generation to set an explicit calendar MIME type.
• Add PHPUnit coverage for EmailService attachment clearing and MIME passthrough.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/lib/Email/EmailServiceTest.php	Adds unit tests for clearing attachments per send and passing MIME type into PHPMailer.
tests/fakes/FakeEmailMessage.php	Introduces a minimal IEmailMessage fake that supports string attachments + optional MIME type.
tests/fakes/TestReservationEmailMessage.php	Adds a reservation-email fake intended to expose ICS attachment generation for testing.
tests/fakes/namespace.php	Registers new fakes in the global test bootstrap.
lib/Email/IEmailMessage.php	Extends the interface to accept/return attachment MIME type.
lib/Email/EmailMessage.php	Stores and exposes the optional attachment MIME type.
lib/Email/EmailService.php	Clears attachments before each send and forwards MIME type to PHPMailer.
lib/Email/Messages/ReservationEmailMessage.php	Sets the ICS attachment MIME type to text/calendar; charset=UTF-8; method=REQUEST.

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