tui: highlight serving service state

[edwin-zvs]

Summary

• highlight the service-view serving state in the success color with bold text
• keep paused state visible with the warning color and preserve selected-field highlighting
• add a focused TUI rendering test for the serving state

Verification

• cargo test -p construct-cli service_view_highlights_the_serving_state --no-fail-fast
• cargo build

The only produced workspace binary is target/debug/construct.