fix(tui): show full command in preview instead of truncating

[JoseVelazcoH]

Summary

The TUI preview pane cut long commands to a single line with an ellipsis. Now the command is shown in full, wrapped across as many lines as needed.

Motivation

A long command (e.g. git fetch ... && git checkout <long-branch>) was truncated in the preview, so you couldn't read what you were about to run or replay.

Changes

• Stop truncating the command line in render_preview; rely on the paragraph's existing Wrap to lay it out across lines.
• Add a TestBackend test asserting the tail of a long command is visible in the preview.

Test plan

• Unit tests added / updated (660 passing)
• Integration tests added / updated
• Tested locally with cargo test
• Manual: rendered preview buffer shows the full wrapped command

Review checklist

• Follows commit convention
• No raw SQL without parameterized queries
• No ORM or migration library introduced
• cargo fmt and cargo clippy clean (pre-existing search.rs MSRV warning unrelated)
• Docs updated if public API changed (n/a)

Breaking changes

None.