feat: support custom skill sources

skiff/project.py

@@ -65,13 +65,16 @@ def add_skill_to_manifest(
         file_path = path
 
     entries = [normalize_skill_entry(e) for e in data.get("skills", [])]
-    if any(e["name"] == name for e in entries):
-        return
-
     item: dict[str, Any] = {"name": name, "source": source}
     if extra:
         item.update(extra)
-    entries.append(item)
+    existing_index = next((i for i, entry in enumerate(entries) if entry["name"] == name), None)
+    if existing_index is None:
+        entries.append(item)
+    elif entries[existing_index] == item:
+        return
+    else:
+        entries[existing_index] = item
 
     data["skills"] = [_entry_to_yaml(e) for e in entries]
     save_manifest(file_path, data)