fix test breakage from https://github.com/dyad-sh/dyad/pull/2155

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## Summary by cubic
Adjusted chat mode selection in e2e tests to match updated UI labels and
prevent failures. Uses "Agent v2" and "Build with MCP" instead of the
old "(experimental)" labels.

<sup>Written for commit 22342fd91b4708311796b51552b0106acea66b9b.
Summary will update on new commits.</sup>

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