Merge master: pluggable storage, and a name that anchors

Conflicts were docs/traceability.md alone, and it is generated — so it
was regenerated rather than hand-merged. dr-face was untouched on the
other side; ui/dr-ui/src/faces.rs and identity_ui.rs auto-merged, the
first around recluster's anchoring and the second around load_faces.

Worth recording because the two branches met on the same problem from
different ends. Master's "Let a name hold a group together" is the fix
for the sixteen Catherines — fourteen of them empty — that this branch
found while measuring the library and reported without fixing.

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

ui/dr-ui/src/identity_ui.rs

@@ -355,15 +355,10 @@ fn to_slint_image(width: u32, height: u32, rgba: &[u8]) -> slint::Image {
 /// boundary would not be.
 /// What the whole-library face pass needs to reach the server.
 ///
-/// Credentials and not just paths, because the pass fetches its own pixels: an
+/// A connection and not just paths, because the pass fetches its own pixels: an
 /// image with no proxy is the ordinary case, not one to skip (see
 /// `library::spawn_face_sweep`).
-pub type SweepPaths = (
-    dr_sync_nextcloud::AppCredentials,
-    String,
-    std::path::PathBuf,
-    std::path::PathBuf,
-);
+pub type SweepPaths = (dr_sync::Connection, std::path::PathBuf, std::path::PathBuf);
 
 /// The detector and embedder files, when both are present.
 pub type ModelPaths = (std::path::PathBuf, std::path::PathBuf);
@@ -689,7 +684,7 @@ pub fn wire<S, M, P>(
             if ctl.regroup.borrow().is_some() {
                 return;
             }
-            let Some((_, _, catalog_path, _)) = paths() else {
+            let Some((_, catalog_path, _)) = paths() else {
                 return;
             };
 
@@ -781,7 +776,7 @@ pub fn wire<S, M, P>(
                 w.set_identity_model_missing(true);
                 return;
             };
-            let Some((creds, user_id, catalog_path, store_dir)) = paths() else {
+            let Some((conn, catalog_path, store_dir)) = paths() else {
                 return;
             };
 
@@ -790,8 +785,7 @@ pub fn wire<S, M, P>(
             *ctl.activity.borrow_mut() =
                 Some(activity.begin(crate::activity::Kind::Index, "Indexing faces"));
             *ctl.sweep.borrow_mut() = Some(crate::library::spawn_face_sweep(
-                creds,
-                user_id,
+                conn,
                 catalog_path,
                 store_dir,
                 detector,