The cold-scan progress line was gated only on stderr.isTTY, which is also
true when the interactive dashboard and `codeburn compare` render Ink to
the same terminal — so the \r progress line printed over their frame and
garbled the screen (confirmed under a PTY). isTTY alone can't tell an Ink
UI apart from a plain CLI command.
Gate on an explicit 'interactive Ink UI is live' flag instead: the two
interactive entrypoints call setInteractiveScanUI() before they render, so
their scans (and the dashboard's 30s auto-refresh, including the
getPlanUsages -> parseAllSessions path) stay silent, while plain CLI
commands (overview, export, status) still show progress. Verified under a
PTY: dashboard and compare silent, overview shows progress, piped/non-TTY
silent. Adds a gate unit test covering the interactive-active, plain-TTY,
non-TTY, threshold, and finish()-clear cases.
