Fix portability audit cold-cache handling

[Quim Muntal (qmuntal)]

Summary

• Treat absent optional audit history as an expected cold start: continue without prior history and do not emit missing_data for that case, following github/gh-aw#53122.
• Write the audit record through the existing edit tools into gh-aw's pre-created cache directory. No initialization step or additional shell permission is needed.
• Preserve live GitHub history checks and existing failure reporting.

Fixes #1254.

Validation

• Strict compilation with the repository-pinned gh-aw v0.89.21 passed twice with zero warnings and byte-identical generated output.
• Whitespace and exact two-file scope checks passed; no SDK source, tests, or binary artifacts are included.
• No hosted workflow rerun was dispatched.

Generated lock

The regenerated lock also emits the existing CLI-proxy digest from the shared action lock into the agent and detection configurations. Runtime versions, permission settings, safe-output guards, and shared pins are unchanged.

[Copilot]

Copilot review overview

🟢 Approval recommended

Existing cache setup and permissions support the narrow change, with no unresolved findings or weakened audit safeguards.

Review effort: Balanced
Findings: None

What changed in this PR

Fixes #1254 by treating missing optional history as a normal cold start in the weekly .NET-to-Go portability audit.

Changes:

• Suppresses missing_data for absent cache history and directs writes through existing edit tools.
• Regenerates the workflow lock, including the existing shared CLI-proxy pin, while preserving live history checks and failure reporting.

File	Description
.github/​workflows/​dotnet-code-portability-weekly.md	Clarifies cold-start handling and cache writes.
.github/​workflows/​dotnet-code-portability-weekly.lock.yml	Updates the source hash and emits the shared CLI-proxy pin.

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