Fix circular dependency error message to show actual cycle path

The error was hardcoding [pkg_key, pkg_key] regardless of actual cycle.
Now tracks the path through dependencies to report the real cycle.

backend/app/dependencies.py

@@ -698,6 +698,8 @@ def resolve_dependencies(
     # Track visiting/visited for cycle detection
     visiting: Set[str] = set()
     visited: Set[str] = set()
+    # Track the current path for cycle reporting (artifact_id -> pkg_key)
+    current_path: Dict[str, str] = {}
     # Resolution order (topological)
     resolution_order: List[str] = []
 
@@ -719,8 +721,10 @@ def resolve_dependencies(
 
         # Cycle detection (at artifact level)
         if artifact_id in visiting:
-            # Build cycle path
-            raise CircularDependencyError([pkg_key, pkg_key])
+            # Build cycle path from current_path
+            cycle_start = current_path.get(artifact_id, pkg_key)
+            cycle = [cycle_start, pkg_key]
+            raise CircularDependencyError(cycle)
 
         # Conflict detection - check if we've seen this package before with a different version
         if pkg_key in version_requirements:
@@ -751,6 +755,7 @@ def resolve_dependencies(
             return
 
         visiting.add(artifact_id)
+        current_path[artifact_id] = pkg_key
 
         # Track version requirement
         if pkg_key not in version_requirements:
@@ -807,6 +812,7 @@ def resolve_dependencies(
             )
 
         visiting.remove(artifact_id)
+        del current_path[artifact_id]
         visited.add(artifact_id)
 
         # Add to resolution order (dependencies before dependents)