refactor: use mailbox id instead of role everywhere in ui

[krantheman]

• routing
• actions
• APIs

[Copilot]

Pull Request Overview

This PR refactors the mail system to use mailbox IDs instead of roles throughout the UI. This change improves data consistency by using unique identifiers rather than role strings for mailbox operations.

• Replaces mailbox_role field references with mailbox_id in email search and storage operations
• Updates API endpoints to accept and work with mailbox IDs instead of roles
• Modifies frontend components to use mailbox IDs for routing, filtering, and UI state management

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
mail/mail/doctype/email_message/search.py	Updates search indexing to use mailbox_id field instead of mailbox_role
mail/mail/doctype/email_message/email_message.py	Changes realtime event publishing to use mailbox_id
mail/api/mail.py	Refactors API functions to work with mailbox IDs and removes role-to-ID conversion calls
frontend/src/stores/user.ts	Adds helper function to convert mailbox roles to IDs
frontend/src/router.ts	Updates default route to use mailbox ID
frontend/src/pages/MailboxView.vue	Converts mailbox role checks to use IDs throughout component
frontend/src/components/Modals/SearchModal.vue	Updates search result navigation to use mailbox_id
frontend/src/components/MailThread.vue	Replaces role-based filtering with ID-based filtering
frontend/src/components/HeaderActions.vue	Changes mailbox comparisons to use IDs
frontend/src/components/AppSidebar.vue	Updates navigation links to use mailbox IDs