fix(tui): let mouse capture keep history arrows on Windows

[Hmbown]

Summary

• removes the blanket Windows override from the empty-composer arrow default
• keeps the scroll fallback when mouse capture is off, including Windows conhost-style terminals
• updates the config comment and regression coverage for both Windows default cases

Fixes #1720

Credit: harvests the focused behavior from Lee-take's #1866 and Paulo's Windows terminal matrix in the issue thread.

Validation

• cargo fmt --all -- --check
• CARGO_TARGET_DIR=/Volumes/VIXinSSD/whalebro/codewhale-target/issue-1720 cargo test -p codewhale-tui composer_arrows_scroll_default

[gemini-code-assist]

Warning

You have reached your daily quota limit. Please wait up to 24 hours and I will start processing your requests again!

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.