Make Ctrl/Cmd+Enter steer active chats

[hamzamerzic]

Summary

• make Ctrl/Cmd+Enter steer newly composed text into an active response when steering is available
• keep plain Enter's existing queue behavior and fall back to normal sending when there is no steerable live turn
• preserve the existing pending-question, connection, and durability safeguards so a racing or failed steer leaves the message safely queued

Testing

• 28 focused frontend tests
• npm run build
• manual browser verification with mocked message and stream requests
• adds Playwright coverage for the exact Ctrl+Enter queue-to-steer flow

[hamzamerzic]

Closing as superseded by #118. The two PRs implement the same durable queue→steer behavior, but #118 also dereferences the current steer handler after the queue acknowledgement and synchronously suppresses duplicate modified-Enter submissions while that acknowledgement is in flight, with a held-ack regression test.