feat: add tested prompt tournament dashboard

[OgeonX-Ai]

Summary

• add dashboard UI and API routes for A/B prompt tournaments
• persist tournament results in EventStore with schema support
• harden tournament mutation with same-origin, JSON, and non-empty prompt validation
• add isolated EventStore, dashboard API, UI, route, and failure-path tests

Verification

• git diff --check
• npm.cmd run test:coverage
• npm.cmd run release:verify

Coverage: 52 test files, 387 tests, 100% statements/branches/functions/lines.

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