Progress output pollutes logs when stdout is not a TTY (playground/cluster downloads)

[alastori]

• TiUP version: v1.16.4 (darwin-arm64)
• Component versions: playground nightly (v9.0.0-beta.2.pre-nightly)
• Environment: macOS; running tiup from a shell, redirecting stdout/stderr to files (non-TTY)

Steps to reproduce:

1. Run: tiup playground nightly --without-monitor --mode tidb --db 1 --kv 1 --tiflash 0 --pd 1 --tag logtest2 >playground.log 2>&1
2. Open playground.log.

Actual result:

• Log contains cursor-control escape sequences and progress-overwrite junk, e.g. \x1b[1A\r\x1b[2K- TiDB: 127.0.0.1:4000 ... Done\x1b[1B\r\x1b[2K.
• Download progress lines are glued together on one line (no newlines).
• CI=true, NO_COLOR, or piping through tr '\r' '\n' do not prevent the cursor-move escape sequences. Playground has no --format/plain mode.

Expected result:

• When stdout is not a TTY, progress/spinners and cursor movements should be disabled or reduced to plain one-line updates so redirected logs are clean.

Known workarounds:

• For cluster commands only: --format plain/--format json avoids starting the spinner loop.
• For playground/download output: only post-processing helps today (col -b or sed 's/\x1b\[[0-9;]*[A-Za-z]//g'); there is no built-in plain/CI mode.

Notes:

• A minimal TTY check and auto-switch to plain when stdout is not a terminal (or a --no-progress/--ci flag) would address this.