fix(tui): echo the expanded paste, not the [[ … ]] label

[ericleepi314]

Problem

Pasting a long query collapses it in the composer to [[ Create a persist.. [14 lines] .. ard for follow-up questions. ]]. On submit the backend got the expanded text, but the transcript echo showed the label.

Fix

• useSubmission.send echoes the expanded text. User rows over 10k chars render CC-style (UserPromptMessage.tsx): 2.5k head + … +N lines … + 2.5k tail. virtualHeights estimates on the same truncation.
• /retry now re-sends the expanded text; before, it sent the bare label after clearIn() had dropped the snippets.
• Busy, no-session, steer-rejected and session busy submits used to lose the paste. The queue keeps the label, and its snippets are carried in a ref until the message is sent. This way {!cmd} interpolation in sendQueued never runs over pasted content.

Tests

• New useSubmissionPasteEcho.test.ts has 9 tests. 6 of them fail on the old useSubmission.ts.
• tsc is clean.
• The full vitest suite has the same 8 failures that are already on main (createGatewayEventHandler, cursorDriftRegression, statusRule, useConfigSync, virtualHeights compound-width).
• The critic subagent approved the core fix and the busy/steer path. The session busy re-queue fix and its tests were added after that approval and were not re-reviewed.

Follow-ups (not in this PR)

• History recall (↑) holds the label, and its snippets are gone.
• carriedSnips isn't cleared on session new/resume. It's capped at 32 snippets / 4 MB.
• A paste starting with {!…} puts an interpolation token into the label (edge preview).

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