Add debug headers to interceptor

[google-labs-jules]

Instruments the interceptor edge function with X-Cpt-Flow, X-Cpt-Token-Status, and X-Cpt-Origin-Status headers. This allows the user to trace the request path and determine if the 401 Unauthorized response originates from the interceptor logic or the upstream backend.

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PR created automatically by Jules for task 2701873894220485395 started by @OsakaLOOP

[google-labs-jules]

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