feat: add super admin bypass in tree list filter

Super admins now see all trees regardless of ownership, team, or
public/default status. Previously the build_tree_access_filter function
had no super_admin check, so admins could only see their own trees plus
public/default/team trees.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/tests/test_trees.py

@@ -172,6 +172,37 @@ class TestTrees:
         active_ids = [tree["id"] for tree in active_trees]
         assert test_tree["id"] not in active_ids
 
+    @pytest.mark.asyncio
+    async def test_super_admin_sees_all_trees(
+        self, client: AsyncClient, auth_headers: dict, admin_auth_headers: dict
+    ):
+        """Test that super admin can see all trees including private ones from other users."""
+        # Create a private (non-public, non-default) tree as a regular user
+        tree_data = {
+            "name": "Private User Tree",
+            "description": "Only visible to author and super admin",
+            "tree_structure": {
+                "id": "root",
+                "type": "solution",
+                "title": "Private",
+                "description": "Private tree"
+            },
+            "is_public": False,
+            "is_default": False
+        }
+
+        create_response = await client.post(
+            "/api/v1/trees", json=tree_data, headers=auth_headers
+        )
+        assert create_response.status_code == 201
+        private_tree_id = create_response.json()["id"]
+
+        # Super admin should see it in list
+        list_response = await client.get("/api/v1/trees", headers=admin_auth_headers)
+        assert list_response.status_code == 200
+        tree_ids = [t["id"] for t in list_response.json()]
+        assert private_tree_id in tree_ids
+
     @pytest.mark.asyncio
     async def test_create_tree_unauthorized(self, client: AsyncClient):
         """Test that creating a tree without auth fails."""