faces: log at the three 503 paths in update_face_handler

PATCH /image/faces/{id} can return 503 from three places (face client
disabled, transient embed error, mid-flight disable) and none of them
were logging — operator sees the status code but nothing in the Rust
log explaining why. Add warn! lines at each so future bbox-edit
failures aren't silent. Response body is unchanged so existing clients
keep working.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/faces.rs

@@ -2311,6 +2311,12 @@ async fn update_face_handler<D: FaceDao>(
     let mut new_embedding: Option<Vec<u8>> = None;
     if let Some((bx, by, bw, bh)) = bbox_patch {
         if !face_client.is_enabled() {
+            warn!(
+                "PATCH /image/faces/{}: 503 — face client not enabled \
+                 (APOLLO_FACE_API_BASE_URL / APOLLO_API_BASE_URL both unset). \
+                 Bbox edit requires Apollo to re-embed.",
+                id
+            );
             return HttpResponse::ServiceUnavailable()
                 .body("face client disabled — bbox edit requires Apollo");
         }
@@ -2387,9 +2393,19 @@ async fn update_face_handler<D: FaceDao>(
                 );
             }
             Err(FaceDetectError::Transient(e)) => {
+                warn!(
+                    "PATCH /image/faces/{}: 503 — Apollo face client transient \
+                     error during re-embed: {}",
+                    id, e
+                );
                 return HttpResponse::ServiceUnavailable().body(format!("{}", e));
             }
             Err(FaceDetectError::Disabled) => {
+                warn!(
+                    "PATCH /image/faces/{}: 503 — face client became disabled \
+                     mid-flight",
+                    id
+                );
                 return HttpResponse::ServiceUnavailable().body("face client disabled mid-flight");
             }
         }