feat: add dex_report_date to AssetCreate model + test for no_dex_days filter

- Add dex_report_date field to AssetCreate Pydantic model
- Include dex_report_date in _build_asset_insert columns/values
- Add test_list_assets_filter_no_dex_days test (11/11 pass)

tests/test_server.py

@@ -1777,6 +1777,15 @@ class TestListAssetsExtendedFilters:
         assert len(data) == 1
         assert data[0]["name"] == "Match"
 
+    def test_list_assets_filter_no_dex_days(self, client):
+        """no_dex_days=N returns assets with no dex report or older than N days."""
+        client.post("/api/assets", json={"machine_id": "DEX1", "name": "HasDex", "dex_report_date": "2026-05-23"})
+        client.post("/api/assets", json={"machine_id": "DEX2", "name": "NoDex"})
+        r = client.get("/api/assets?no_dex_days=5")
+        data = r.json()
+        assert len(data) == 1
+        assert data[0]["name"] == "NoDex"
+
 
 # ─── Phase C: Users API ──────────────────────────────────────────────────