Implement Regression Detection UI

[aviralgarg05]

Description

The "Regression Report" section in src/agentunit/dashboard/app.py has a TODO to "Implement regression detection UI".
Currently it just shows an info message "Configure regression detection settings".

Source

https://github.com/aviralgarg05/agentunit/blob/main/src/agentunit/dashboard/app.py#L374

Task

• Design and implement UI for configuring regression detection.
• Implement the actual regression detection logic (or link to backend logic if separate).