feat(explorer): list one folder level with recursive counts

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/guara-core/src/service.rs

@@ -359,6 +359,13 @@ impl Engine {
         Ok(json!({ "total": total, "items": page }))
     }
 
+    /// One level of the folder tree (see [`crate::explorer::browse`]).
+    pub fn browse(&self, id: &str, path: &str, q: &Query) -> Result<Value> {
+        let j = self.job(id)?;
+        let s = j.st.lock().unwrap();
+        Ok(crate::explorer::browse(&s.found, path, q))
+    }
+
     /// Sidebar navigation facet counts (categories, dates, folders, cameras).
     pub fn facets(&self, id: &str) -> Result<Value> {
         let j = self.job(id)?;
@@ -1232,6 +1239,17 @@ impl Engine {
                     .and_then(|v| v.as_u64())
                     .ok_or_else(|| Error::msg("id ausente"))?
             )?),
+            "browse" => {
+                let q: Query = p
+                    .get("query")
+                    .cloned()
+                    .filter(|v| !v.is_null())
+                    .map(serde_json::from_value)
+                    .transpose()?
+                    .unwrap_or_default();
+                let path = p.get("path").and_then(|v| v.as_str()).unwrap_or("");
+                self.browse(&s("job")?, path, &q)?
+            }
             "results" => {
                 let q: Query = p
                     .get("query")