Code-review follow-ups on the pgvector spike:
- self-similarity sanity check now compares to the seed's own self-distance
(0 for cosine/L2, ~-1 for inner product <#>) instead of a hardcoded ~0, so it
no longer misfires if Immich ever uses a vector_ip_ops index (correctness P3).
- mark the deliberate raw-SQLite read in the probe as a spike-only exception and
add an M1.5 TODO that the real pgvector reader belongs in shared/photoflow/immich
and SQLite access in shared/photoflow/core (project-standards P2 x2).
- document join_and_coverage's return shape; extract a _pct() helper to dedupe the
coverage-percentage formatting (maintainability P3 x2).
Findings doc refreshed from the latest live run (coverage now ~46%, re-run ongoing).