fix(tmux): look for a dialog before pressing Enter on a delivered paste

[tfyl]

Why

Gate Inbox sometimes answers a Claude Code question on its own, ticking a multi-select box, picking a single-select option, or submitting a stepper's review page, when no one chose anything. Each time, the agent then carries on with an answer the user never gave.

Summary

• The poll pass decides a pane may take a message from a capture taken before the paste. Up to a second later it presses Enter without looking at the pane again. Claude Code takes messages mid-turn, so the agent can put a question up in between. The dialog swallows the paste, the echo never arrives, the paste window runs out, and the Enter lands on the row under the dialog's cursor.
• SendTextAsync now takes a hold check that the driver runs on a fresh capture just before the Enter. When it reports a dialog, the Enter is not pressed and the send settles with ErrSubmitHeld. The message is then dropped the way any failed send is, and its sender is told.
• The poller's check is the same rule test safeToInterrupt already uses: the session's rules match a waiting state. All three async senders (queued messages, pending inputs, the usage-limit continuation) get it. The synchronous SendText is unchanged.
• Trade-off: a message whose own pasted lines quote a dialog legend can trip the hold and be dropped. A dropped message is reported to its sender; an answered dialog is not reported to anyone.
• This complements fix(status): hold queued messages on a Claude question whose legend wraps #308, which makes the rules recognise a question whose legend or review line wraps in a narrow pane. This PR covers a dialog that appears after the check.

Test plan

• TestSendTextAsyncLeavesTheEnterUnpressedOnADialog: against a real tmux pane showing a legend with echo off, the paste arrives, the submit settles with ErrSubmitHeld, and no carriage return reaches the pane. It fails with the guard disabled (submit = <nil>).
• The existing SendTextAsync tests pass with a nil hold.
• go vet ./... clean. The full suite passes all 68 packages on a scratch TMUX_TMPDIR.

🤖 Generated with Claude Code