Feature/issue 145 share actions resend email

[perezjnr]

Recipient management for shares (initial implementation)

This only details with part one of the issue, as it's best to split features into different PRs

This change introduces recipient management for file shares, allowing sharers to view, add, edit, remove, and resend share invitations after a share has been created.

Recipient email addresses are stored only for the lifetime of the share and are automatically removed when a share expires, keeping data retention minimal. Recipient names are optional and, when provided, are used to personalise email greetings. Email addresses remain the unique identifier per share to prevent duplicates.

The functionality is available from both My Shares and All Shares via a shared recipients modal, avoiding duplication of logic and keeping behaviour consistent across views. Existing authorisation checks are respected so that only users who can manage a share may modify its recipients.

This implementation focuses on core functionality and correctness. There will be further improvements as part of this issue, including refinement of the user experience, validation and error handling, and alignment with Vue best practices.

Note: I am not a Vue specialist, and parts of the frontend were developed with the assistance of AI. Suggestions for improving structure, patterns, or maintainability are very welcome.