Remove the review screen's Draft/Re-draft button; route re-drafting through the conversation #153

Every item comes from the Proclaim slide feeder, and the service already drafts each one ahead of time through /api/translateItem (writing the agent conversation and its notes under the item's id). The review screen's Draft / Re-draft button (formerly "Suggest") calls the same endpoint from the browser, but:

• it omits existingTranslation (the Proclaim French screen text the service passes as grounding), so the re-draft is worse than the one the service produced;
• it writes a fresh conversation under the same itemId, discarding the service's conversation and the translator notes on it;
• the pasted-text case it was designed for (no itemId, so the worker never sees it) does not exist in practice.

What it still covers today: an item the service hasn't reached yet, or the service being down. Both are better served by the conversation panel — "please re-draft the Creole" as a follow-up keeps the grounding and the notes — plus a visible "not drafted yet" state that points at the service.

Plan:

1. Make sure a follow-up message on an item with no conversation can bootstrap one (today sendConversationMessage needs an existing conversation).
2. Remove handleDraft, the button, and the draftTranslations / redraftTranslations / drafting strings.
3. Reconsider whether the browser needs /api/translateItem at all after that (it's the last caller outside the service).

Context: review discussion on #152.