Fix/annex mailer admin view

[tsubik]

Fix annex mailer crash for history-only annexes

Sentry: undefined method 'name_with_fmu' for nil in document_valid.html.mjml.

Cause

When an operator uploads a new version of a document (or the document is
destroyed), OperatorDocument#disconnect_annexes drops the annex→document
join rows, keeping only the join to OperatorDocumentHistory. From then on
annex.operator_document is nil, while annex.operator still resolves via
the history — so notify_about_changes passes its operator.present? guard,
the mail is sent, and the views blow up on the nil document. Admins can still
approve/reject such annexes from the annex list, which is what triggered it.

Changes

• OperatorDocumentAnnex#related_operator_document — the live document, or
  the last history entry. #operator and #operator_document_name now go
  through it, so the notification guard and the mail body use the same object.
• OperatorDocumentHistory#name / #name_with_fmu, mirroring OperatorDocument.
• Mailer assigns @operator_document / @operator_document_name once; the six
  annex mail views use them.
• History-based documents are labelled (History version) — in the mails
  (translated: en/fr/es) and in the Documents column of the admin annex list,
  which now also links to the history record instead of rendering blank.

Tests

• spec/mailers/operator_document_annex_mailer_spec.rb — all three mails, with
  the annex attached and history-only, plus the fr translation of the suffix.
• spec/controllers/admin/operator_document_annexes_controller_spec.rb — the
  Documents column in both states.