fix: allow expanded lists to collapse

[Tryanks]

Summary

• keep the sidebar thread-list toggle visible after expansion and relabel it as Show less
• keep the previous-log toggle visible after expansion with a collapse label and upward chevron
• make locale files explicit compiler inputs so incremental builds embed new translations
• document the reversible controls and add English/Chinese regression coverage

Verification

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo build
• cargo test --workspace
• isolated native-app click regression for both expand/collapse flows