Snapshot redaction strips styles/padding (reduced coverage)

[laynepenney]

Problem: TUI exec_cell snapshots are stabilized by redacting styles and normalizing right-edge padding, which removes alignment/style regressions from coverage.

Context: tests/tui_exec_cell.rs now strips the styles block and trims spaces before the right border to avoid flaky diffs.

Expected behavior:

• Keep deterministic snapshots without losing style/spacing coverage, or add a separate style/alignment-focused snapshot.

Files involved: codi-rs/tests/tui_exec_cell.rs