Keep composer drafts until message queue acceptance

[Xare123]

Problem

The composer could clear before the asynchronous send handler accepted a message, making a rejected or stalled send appear to lose the draft.

Change

Await the composer action handler before clearing text and reply state. Failure leaves the draft intact; successful queue acceptance clears it once.

Validation

Focused Flutter tests pass: 2/2 for handler completion and unavailable-handler failure.

Non-goals

This does not change URL parsing, transport retry policy, CloudKit, or attachment downloading.