Defer environment updates to prevent UI blocking

[mohrad-oishii]

This PR defers environment update operations in JointTrajectoryWidget to prevent UI blocking when the current row changes. The changes use QTimer::singleShot() to delay EnvironmentManager::set() and setState() calls by 100ms, allowing the UI thread to process other events first.

• Defer EnvironmentManager::set() calls in three locations within onCurrentRowChanged() using QTimer::singleShot() with a 100ms delay
• Defer setState() calls to avoid blocking from currentStateChanged() event broadcasts
• Capture variables by value in lambda closures to ensure proper lifetime manag