Improve workspace distinction and persist active terminal blocks

[mmaxiaolei]

Summary

• Refine repository workspace UI styling and spacing for clearer workspace distinction.
• Remove redundant workspace hierarchy divider styling.
• Persist active terminal blocks during application shutdown so unfinished Claude sessions remain visible after restart.

Validation

• cargo test -p warp active_block_can_be_finalized_for_shutdown --lib
• cargo check -p warp
• macOS app bundle built and codesign verification passed.