Improve the prompt for the "modes" e2e test

[cte]

Description

This test seems to flake a lot, but this prompt seems a bit more stable.

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Important

Improves stability of "modes" e2e test by updating the prompt and simplifying test logic in modes.test.ts.

• Test Stability:
  • Update prompt in modes.test.ts to "For each of architect, ask, and debug use the switch_mode tool to switch to that mode."
  • Simplifies test logic by removing unused variables and listeners.
• Assertions:
  • Verifies modes array includes "architect", "ask", "debug" and has length 3.

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