server: reduce log noise and fix inbound webhook fanout crash

[willwashburn]

Summary

• reduce noisy request logging for expected client errors on /v1/ws 401 and /mcp 400/406 with suppression plus sampling
• add actionable structured request metadata (status_class, route_group, auth_scheme, error_code, hashed fingerprints)
• fix fanout webhook.received crash by allowing fanoutToChannel to accept an explicit workspace id when context workspace is absent
• add regression tests for logging middleware behavior and fanout workspace override

Validation

• npm --prefix packages/server test

Notes

• Latest production error investigated: TypeError: Cannot read properties of undefined (reading id) on /v1/hooks/:webhookId background fanout path.

[github-actions]

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Environment	URL
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Observer	https://pr39-observer.relaycast.dev

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