fix(email): Draft re-appears after send

[evanhutnik]

Summary

• Fix draft re-appearing after send: After sending a reply, navigating away from the thread, and coming back, the compose box would incorrectly restore the sent message as an active draft. This was caused by the undo-send snapshot (undoReplySnapshot) persisting at module level and being auto-restored on remount.
• Ensure draft is always saved before send: Previously, if the user typed a reply and hit send before the 1-second debounce fired, no draft existed on the server, so undo-send had nothing to restore. Now we await executeSaveDraft() before sending to guarantee a draft ID always exists.
• Fix undo-send after navigating away: The undo toast's onClick held a closure over the old component instance, so clicking undo after navigating away and back would unsend the message but fail to restore the compose box. Introduced a module-level restoreUndoCallback that the current component registers, allowing stale closures to reach the live component.

Changes

• Split the single undoReplySnapshot into two module-level variables: undoSendSnapshot (set on send, consumed by undo) and undoReplySnapshot (only set by undo for inline reply remount)
• Added restoreUndoCallback pattern so undo-send works correctly across component remounts
• Deferred restore via setTimeout to let reactive updates from setQueryData settle before restoring attachments
• Removed redundant executeSaveDraft() call in the scheduled send path since draft is now always saved before send

[github-actions]

Preview: https://evan-draft-sticks-around-saevyo.preview.macro.com/app (6326352)