ci: compile production C# with exact runtime references

[Nico77600]

Changes

• Replace the loose-source C# no-build pilot with an advisory manual compiler build inside the CodeQL tracer lifecycle.
• Compile every production source against the running PowerShell framework and required exact shipped SQLite/PowerShell assemblies.
• Avoid NuGet feed inference/restores, compiler sharing and incremental-build omissions.
• Verify and preserve source/reference manifests with the already approved pinned upload-artifact action.
• Preserve existing event/fork guards, minimal permissions, approved pins, SARIF upload semantics, runtime source and packaging.

Validation

8/8 production C# sources compiled locally; exact source/reference inventories and hashes matched.
Existing SDK Roslyn MSBuild task; no new tooling installed and no runtime code executed.
Local compilation is prerequisite evidence only: complete hosted extraction remains pending tracer/database diagnostics.
CodeQL does not analyze PowerShell; the existing PowerShell validation remains in force.