fix(cli): use datetime() for CodeLink.added_at in tests (mypy strict)

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

tests/cli/test_cli.py

@@ -6,6 +6,7 @@ so the suite runs offline without real API calls.
 
 from __future__ import annotations
 
+from datetime import datetime
 from typing import Any
 from unittest.mock import MagicMock, patch
 
@@ -193,7 +194,7 @@ class TestProvAddLink:
                 paper_id="2301.07041",
                 role="core_algorithm",
                 note="Primary reference",
-                added_at="2023-01-01T00:00:00Z",
+                added_at=datetime(2023, 1, 1),
             )
             mock_add.return_value = mock_link
 
@@ -231,7 +232,7 @@ class TestProvLinks:
                     paper_id="2301.07041",
                     role="core",
                     note=None,
-                    added_at="2023-01-01T00:00:00Z",
+                    added_at=datetime(2023, 1, 1),
                 ),
                 CodeLink(
                     id=2,
@@ -239,7 +240,7 @@ class TestProvLinks:
                     paper_id="2301.07042",
                     role="utility",
                     note=None,
-                    added_at="2023-01-02T00:00:00Z",
+                    added_at=datetime(2023, 1, 2),
                 ),
             ]