4d6f6f7144
FR-6.4 requires a target with no writable repo to record `filing: unavailable` with its reason in the output. The filing pass knows that; audit-snapshot does not, and `notes` was derived purely from no-offload/drift-note verdicts, so the fact could reach the user's terminal but never the wiki page FR-6.4 points at. Requested by the Phase 6 output-paths work.