Adopt faces a hundred images per commit, and hold one generation per image in the shards

The shard import recorded each adopted image in its own transaction:
fourteen thousand commits, and fourteen thousand turns at the write lock
that every read on the UI thread queued behind — the sync was felt as a
laggy grid and as "database is locked" from whichever writer lost the
wait. `record_detections_within` takes the caller's transaction, and the
import commits every hundred images.

The store carried every detector generation of an image — 24,123 entries
for 19,089 images on the reference library, a third of its 293 MB — when
only the strongest is ever adopted. A put now skips a pass a held one
outranks, and retires the passes it outranks from the index; sealed
shards keep their bytes, but nothing is written twice from here.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

core/dr-catalog/src/faces.rs

@@ -279,7 +279,25 @@ pub fn record_detections(
     faces: &[DetectedFace],
 ) -> Result<Vec<FaceId>, CatalogError> {
     let tx = conn.unchecked_transaction()?;
+    let ids = record_detections_within(&tx, image_id, model_id, source_edge, faces)?;
+    tx.commit()?;
+    Ok(ids)
+}
 
+/// [`record_detections`] inside a transaction the caller owns.
+///
+/// For a caller recording many images at once — the shard import adopts
+/// fourteen thousand in one pass — where a commit per image is fourteen
+/// thousand fsyncs and fourteen thousand turns at the write lock that every
+/// read on the UI thread queues behind. `unchecked_transaction` cannot nest,
+/// so the batching has to be offered here rather than wrapped from above.
+pub fn record_detections_within(
+    tx: &Connection,
+    image_id: ImageId,
+    model_id: &str,
+    source_edge: u32,
+    faces: &[DetectedFace],
+) -> Result<Vec<FaceId>, CatalogError> {
     // Everything the old faces knew, so it can be carried across the
     // replacement. Read only when there is something to carry it onto: a
     // pass that found nothing has nothing to match, and decoding a vector
@@ -287,7 +305,7 @@ pub fn record_detections(
     let prior = if faces.is_empty() {
         Vec::new()
     } else {
-        read_priors(&tx, image_id)?
+        read_priors(tx, image_id)?
     };
 
     tx.execute("DELETE FROM faces WHERE image_id = ?1", [image_id.0 as i64])?;
@@ -389,7 +407,6 @@ pub fn record_detections(
         ],
     )?;
 
-    tx.commit()?;
     Ok(ids)
 }