okfgen: the pruning guard compares scope flags, not the scope rule #168

Extracted from ROADMAP.md (producers/OkfProducer follow-ups).

BundleWriter refuses to prune when the previous run covered a wider scope. It decides this by comparing the flags recorded in the manifest, so it is blind to a run whose flags are identical but whose rule narrowed.

Measured: a bundle generated before scope moved to effective visibility was regenerated with the same flags. It lost five concepts and the guard stayed silent.

The producer now prints a note when it caps a public member at an internal container, which covers today's only case.

General fix: record a scope-rule identifier beside scope in the manifest, so that the existing guard fires on a rule change. This changes the manifest format, which is a compatibility decision of its own.

The producer is outside CI: run dotnet test producers/OkfProducer.sln.