[AI] Expand Test Coverage - mcp

[KCarretto]

Expanded test coverage for the tavern/internal/mcp module by adding proper testing of the MCP tool handlers (list_hosts, list_quests, create_quest, etc.), which were previously only mocked in database data without handler execution.

Coverage for this package went from ~16% to 70.6%.

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PR created automatically by Jules for task 18016252472236369391 started by @KCarretto

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