test(e2e): mock missing API routes for tests

[ManupaKDU]

This PR implements the missing mock handlers inside api-mocker.ts for endpoints /api/review, /api/stats/history, and /api/event_ids, addressing the TODO(real-bug) comments in error-allowlist.ts. By returning sensible fixture data (or empty arrays where appropriate), it prevents Vite's preview server from throwing unhandled 500 internal server errors during Playwright tests. The corresponding regex exclusions have been removed from the error allowlist.

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PR created automatically by Jules for task 13503325207137618528 started by @manupawickramasinghe

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