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.

ui/dr-ui/src/identity_ui.rs

@@ -478,6 +478,8 @@ fn push_faces(window: &AppWindow, ctl: &IdentityController, cells: &[FaceCell])
             confirmed: c.confirmed,
             confidence: c.confidence_label().into(),
             crop_px: c.crop_px as i32,
+            quality: c.quality_label().into(),
+            in_gallery: c.in_gallery(),
             picked: picked.contains(&c.face),
         })
         .collect();