Validate hosted delivery of internal token usage logs

[hallvictoria]

Context

PR #147 adds best-effort internal token-usage records through the azure.functions.AgentRuntime INFO logger. Repository tests verify the in-process logger call, but cannot prove delivery through the hosted Azure Functions logging pipeline to the intended internal sink.

Validation

Deploy PR #147 to a representative hosted Function App and invoke at least one primary, delegated, streaming, unavailable-usage, and workflow Sub Agent call.

• Confirm each expected Agent token usage: {json} INFO record reaches the intended internal sink.
• Record the effective category/level filtering behavior for azure.functions.AgentRuntime.
• Record whether sampling applies and, if so, its configuration and accounting implications.
• Record retry behavior between the Functions host/worker and the sink.
• Record possible duplicate-delivery behavior and the ingestion-side deduplication/aggregation policy.
• Attach redacted query output or another durable evidence link showing the validated records.
• Link the evidence back to FRD 0008 and close its hosted-validation checkbox.

Exit criteria

Hosted delivery semantics are documented with durable evidence, and FRD 0008 no longer has an untracked external merge gate.