feat: include created_at timestamp in search results (closes #465)

Surface the existing filed_at metadata as created_at in search result
objects returned by search_memories(). Enables temporal reasoning over
search hits without additional queries.

Author: sha2fiddy

mempalace/searcher.py

@@ -397,6 +397,7 @@ def search_memories(
             "wing": meta.get("wing", "unknown"),
             "room": meta.get("room", "unknown"),
             "source_file": Path(source).name if source else "?",
+            "created_at": meta.get("filed_at"),
             "similarity": round(max(0.0, 1 - effective_dist), 3),
             "distance": round(dist, 4),
             "effective_distance": round(effective_dist, 4),

tests/test_searcher.py

@@ -51,6 +51,13 @@ def test_result_fields(self, palace_path, seeded_collection):
         assert "source_file" in hit
         assert "similarity" in hit
         assert isinstance(hit["similarity"], float)
+        assert "created_at" in hit
+
+    def test_created_at_contains_filed_at(self, palace_path, seeded_collection):
+        """created_at surfaces the filed_at metadata from the drawer."""
+        result = search_memories("JWT authentication", palace_path)
+        hit = result["results"][0]
+        assert hit["created_at"] == "2026-01-01T00:00:00"
 
     def test_search_memories_query_error(self):
         """search_memories returns error dict when query raises."""