Fix OTLP gRPC authentication metadata

[manas-fortifyroot]

Summary

Fix OTLP/gRPC export failures caused by uppercase metadata keys.

grpcio requires metadata keys to be lowercase. Passing Authorization
caused trace export to fail before the request reached the backend.

Changes

• Vendor the OpenLLMetry correction from immutable tag fr-v0.52.6.35.
• Normalize gRPC metadata for vendored trace, metrics, and log exporters.
• Normalize metadata in Ocelle-owned default metrics and logging exporters.
• Update exporter-construction regression tests.
• Regenerate vendoring provenance and dependency manifests.

HTTP exporter headers remain unchanged.

Validation

• Relevant Ocelle tests: 93 passed.
• Fork exporter tests: 38 passed.
• Full system-test suite on Python 3.10: 24/24 suites passed.
• Full system-test suite on Python 3.12: 24/24 suites passed.
• git diff --check passed.