feat(measure): memorizza tempo di inserimento misura (input_duration_ms)

Colonna nullable su measurements + migration 003, campo opzionale negli
schemi API (create singola e batch), passthrough nel proxy Flask e timer
lato client in task_execute: parte all'attivazione del subtask, si
resetta su auto-advance e navigazione manuale.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/frontend/flask_app/tests/test_measure.py

@@ -80,6 +80,45 @@ class TestSaveMeasurement:
         assert data["id"] == 1
         assert data["pass_fail"] == "pass"
 
+    def test_save_measurement_forwards_input_duration(
+        self, logged_in_client, mock_api_client
+    ):
+        """input_duration_ms is forwarded to the backend payload."""
+        mock_api_client.post.return_value = {"id": 1, "pass_fail": "pass"}
+
+        resp = logged_in_client.post(
+            "/measure/save-measurement",
+            json={
+                "subtask_id": 10,
+                "version_id": 3,
+                "value": 9.95,
+                "input_duration_ms": 4250,
+            },
+            content_type="application/json",
+        )
+        assert resp.status_code == 201
+        payload = mock_api_client.post.call_args.kwargs["data"]
+        assert payload["input_duration_ms"] == 4250
+
+    def test_save_measurement_omits_input_duration_when_absent(
+        self, logged_in_client, mock_api_client
+    ):
+        """Without input_duration_ms the payload sends null (backend default)."""
+        mock_api_client.post.return_value = {"id": 1, "pass_fail": "pass"}
+
+        resp = logged_in_client.post(
+            "/measure/save-measurement",
+            json={
+                "subtask_id": 10,
+                "version_id": 3,
+                "value": 9.95,
+            },
+            content_type="application/json",
+        )
+        assert resp.status_code == 201
+        payload = mock_api_client.post.call_args.kwargs["data"]
+        assert payload.get("input_duration_ms") is None
+
     def test_save_measurement_missing_fields(self, logged_in_client, mock_api_client):
         """Missing required fields return 400."""
         resp = logged_in_client.post(