Keep each face's quality, and never compare against a poor one

The embedder's raw output has a length, and the length is a reading of
how recognisable the crop was: a blur, an occlusion or a hard profile
comes out short. Normalising threw it away. A short vector sits near
the middle of the sphere and matches a little of everyone, which is how
one bad crop bridges two people in a grouping pass.

So the length is kept — the store now holds the raw vector, re-normalised
on load, with the length beside it as `faces.quality` — and a face under
MIN_GALLERY_QUALITY (14) is a probe: measured against the gallery and
placed where it fits, but never what another face is measured against.
Two probes are never paired, and a probe is nobody's evidence for a
confidence. The People screen shows the number as "Quality 17.3", dimmed
below the floor.

Faces indexed before this stored unit vectors and have no reading; they
are admitted to the gallery, and schema V14 forgets the run marker of
every image holding one so the next indexing pass measures them. A
peer's unmeasured shard faces are not adopted, or a sync would write
that marker back.

core/dr-face/examples/faces.rs

@@ -63,15 +63,16 @@ fn main() {
             let embed_ms = t.elapsed().as_secs_f64() * 1e3;
 
             println!(
-                "  [{i}] conf {:.3}  box {:.0},{:.0} {:.0}×{:.0}  crop_px {:.0}  embed {embed_ms:.0} ms",
+                "  [{i}] conf {:.3}  box {:.0},{:.0} {:.0}×{:.0}  crop_px {:.0}  quality {:.1}  embed {embed_ms:.0} ms",
                 d.confidence,
                 d.bbox.0,
                 d.bbox.1,
                 d.width(),
                 d.height(),
                 aligned.source_px(),
+                emb.quality,
             );
-            all.push((path.clone(), i, emb));
+            all.push((path.clone(), i, emb.embedding));
         }
     }
 

core/dr-face/examples/scan_bench.rs

@@ -46,11 +46,13 @@ fn main() {
     );
     for n in sizes {
         let (embeddings, crop_px, images) = population(n);
+        let gallery = vec![true; n];
         let faces = Faces {
             embeddings: &embeddings,
             dim: EMBEDDING_DIM,
             crop_px: &crop_px,
             images: &images,
+            gallery: &gallery,
         };
 
         let start = std::time::Instant::now();