Measure the faces already found rather than finding them again

Every face stored before its quality was kept holds a unit vector, and
V14 forgot the run marker of each image holding one so that the next
sweep would look again. Looking again meant detecting again: a whole
re-detection per image, with every suggestion on it thrown away and the
confirmations carried across by box overlap, to recover one number.

The sweep now has a measuring pass between the proxy repair and the
un-indexed images. It lists every image holding an unmeasured face,
fetches the original once, warps each stored face from the landmarks it
already has, embeds it, and writes the raw vector and its length over
the old row. Ids, boxes and identities are untouched; the marker is
re-written fresh so the sync exports the measured vectors. A face whose
landmarks no longer make a warp is dropped, as detection would have
refused to store it. `faces_unindexed` leaves those images to the
measuring pass, so the V14 deletion no longer costs a second detection.

core/dr-catalog/src/schema.rs

@@ -607,14 +607,20 @@ const V14: &str = r#"
 -- face this rule is not yet protecting anyone from, and the only way to
 -- measure it is to embed it again.
 --
--- So the run markers of every image that holds a face are forgotten, exactly
--- as V12 forgot the runs made against too small a proxy, and for the same
--- reason: the work list is "images with no marker", and an image examined
--- without this number is otherwise indistinguishable from one examined with
--- it. The faces stay where they are and keep drawing the People screen until
--- the next pass replaces them, `record_detections` carries the user's
--- confirmations across by box overlap, and an image that was examined and
--- found empty keeps its marker -- there is nothing on it to re-measure.
+-- The sweep's measuring pass is what does that: `dr_ui::library::
+-- faces_unmeasured` lists every image holding a face with no reading, and
+-- each face is embedded again from the native render with the landmarks it
+-- already has, the raw vector written over the old one (`record_measurements`)
+-- and nothing else touched -- not the id, not the box, not who the user said
+-- it was. The faces keep drawing the People screen throughout.
+--
+-- The run markers of those images are forgotten too, exactly as V12 forgot
+-- the runs made against too small a proxy. The build this shipped in had no
+-- measuring pass yet, and a marker is the one thing that stops a face ever
+-- being looked at again; with the pass in place `faces_unindexed` leaves
+-- these images to it rather than detecting them from scratch, so the
+-- deletion costs nothing -- and an image that was examined and found empty
+-- keeps its marker, since there is nothing on it to measure.
 --
 -- The cost is a re-fetch of every image with a face on it, on the next pass
 -- the user starts. That is a whole-library transfer (FR-NC-6), and it starts