[AI] Expand Test Coverage - tavern/internal/mcp

[KCarretto]

Implemented direct unit tests for internal handlers in the tavern/internal/mcp package using an export_test.go file. This change increases coverage from 16.2% to 70.6%. Tests were run 20 times locally to ensure stability, and the full repository test suite was run to prevent regressions.

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PR created automatically by Jules for task 8029231227488556801 started by @KCarretto

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