Fix: label the close-dialog draft button with the generic Save

[dealerweb]

Summary

The third button of the "Save or discard draft?" dialog wraps onto two lines in several languages, making the button row look broken next to its one-line siblings. Shortening the label fixes this at the root, in every locale at once.

Why

• "Save Draft" is a verb-plus-object label, and in many languages that compound is simply long: German "Entwurf speichern", French "Enregistrer le brouillon", Portuguese "Salvar rascunho", Russian "Сохранить черновик". Any of these can exceed the button width the dialog allows, so the wrapping is not a single-locale glitch but structural.
• The context the object provides is redundant here: the dialog title ("Save or discard draft?") and its message already state that a draft is what would be saved. Within that dialog, a bare "Save" is unambiguous - the same pattern the neighbouring buttons already use ("Cancel", "Discard", not "Discard draft").
• common.save already exists, translated in all 22 locales, and the composer already has the common translator in scope - so the fix is one changed line of code and zero new translations.
• Deliberately not fixed with whitespace-nowrap: on narrow phones that would turn the wrap into horizontal overflow. A short label degrades gracefully everywhere.

Changes

• The dialog's save button uses common.save instead of email_composer.save_draft.
• email_composer.save_draft had exactly this one consumer, so the now-dead key is removed from all 22 locales (verified programmatically: only this key removed, every other value byte-identical).

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation

Checklist

• tsc --noEmit passes (0 errors)
• eslint passes on the changed file
• Translation parity test passes (44/44)
• next build succeeds (exit 0)

Notes for Reviewers

• Resulting button rows, for a feel of the symmetry: en "Cancel / Discard / Save", de "Abbrechen / Verwerfen / Speichern", fr "Annuler / Supprimer / Enregistrer".