Implement rate limiting for analytics and mutation endpoints; update EADME and add tests

[Mkalbani]

closes #117

• added analyticsRateLimiter and mutationRateLimiter
• applied analytics limits to analytics routes, including org analytics
• applied mutation limits to POST / PUT / PATCH / DELETE API requests
• added focused Jest coverage for env config, method scoping, metrics, and non-PII logging
• fixed npm test script to use the explicit Jest config

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[1nonlypiece]

Please resolve the conflicts