mason: hostile-config stripping matrix + nested historian qualifier hole

Red-first: a project-tier historian.opencode.variant / historian.pi.thinking_level
merged onto the user's historian model in resolved config. Nested
prompt/permission/tools at harness, entry, and task depths, and nested
mural.model, were also left in the raw project object.

stripUnsafeProjectConfigFields now uses the full historian migrated_execution
inventory (model, fallback_models, variant, thinking_level) and walks both
harnesses' nested executable sites. The schema-derived matrix enumerates
harness/entry/task shapes so a future schema field without inventory
classification fails the test.

The previous historian unit test treated harness-block qualifiers as safe
project-tier tuning; that assertion encoded the hole, so it now expects those
fields to be stripped.

Co-Authored-By: Alfonso <alfonso@cortexkit.io>