New Search command preview styling

Motivation

The New Search command preview was hard to scan because it rendered as a single colored line inside the run rail.

User-facing change

The command preview now uses the proposal-style terminal block: black background, preserved line breaks, continuation markers, and distinct colors for commands, flags, values, numbers, and the preview comment.

API/IaC diff summary

• Frontend: formatted the display-only command preview into multiple shell-style lines while keeping the Copy button output unchanged.
• API: no changes.
• IaC: no changes.

Validation evidence

• cd /home/moonchoi/dev/elb-dashboard && npm --prefix web run build passed.
• Browser visual check on /blast/submit confirmed the command preview renders as a black multiline terminal block with colored command, flag, value, number, continuation, and comment tokens.