Add repetition setting to playground for consistency testing

[mmabrouk]

Body:

We should add the ability to run test cases multiple times in the playground. This would let users check model consistency directly from the UI.

Problem

Users currently can't test how consistent their prompts are across multiple runs. They need to manually run the same test case several times or write code to do it programmatically.

Proposed solution

Add a repetition setting in the playground configuration. Users would click the configuration icon and specify how many times each test case should run.

Implementation details

The configuration could work like this:

• Add a "Repetitions" field in the playground settings panel
• Default value: 1 (current behavior)
• When set to N > 1, run each test case N times
• Display all N outputs for comparison

Use cases

This helps users:

• Test prompt stability across multiple runs
• Identify prompts or models that produce inconsistent results
• Make informed decisions about temperature and sampling settings