Adds a single-row text input + Send button that pins to the viewport
bottom on every run-detail tab as a placeholder for the future
steering composer (will replace the modal). Renders mutually
exclusive with InterviewDock: the dock takes precedence on blocked
runs with pending questions, otherwise the steer bar shows. Reuses
the existing --fabro-interview-dock-clearance variable so consumers
that already pad for the dock pick up the steer bar's clearance too.
Send is intentionally a no-op for now until the steering API is
swapped over from the modal.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>