feat(map): add batch export and adjust layout alignment

- Implement synchronous offscreen wafer map PNG rendering and CSV summary.
- Add "Batch Export" button to file browser sidebar.
- Adjust trend pane bottom spacer to align with About button when visible.
- Fix type check errors and add pytest coverage for batch export.

tests/test_session_controller.py

@@ -1,8 +1,11 @@
+import json
 from unittest.mock import MagicMock
 
 import pytest
 
+import pygui.backend.controllers.session_controller as session_controller_module
 from pygui.backend.controllers.session_controller import SessionController
+from pygui.backend.models.frame import Frame
 
 
 @pytest.fixture
@@ -194,3 +197,31 @@ def test_export_segment_bad_index(qapp, controller, tmp_path):
     controller.segmentExported.connect(exported)
     controller.exportSegment(99)
     assert exported.call_args[0][0]["success"] is False
+
+
+def test_reset_live_trend_sets_start_time_and_emits_reset(controller, monkeypatch):
+    monkeypatch.setattr(session_controller_module.time, "monotonic", lambda: 100.0)
+
+    reset_seen = MagicMock()
+    controller.trendReset.connect(reset_seen)
+    controller._reset_live_trend()
+
+    assert controller._stream_start_time == 100.0
+    assert reset_seen.called
+
+
+def test_on_live_frame_emits_trend_delta_with_elapsed_seconds(controller, monkeypatch):
+    controller._stream_start_time = 100.0
+    monkeypatch.setattr(session_controller_module.time, "monotonic", lambda: 102.5)
+
+    delta_seen = MagicMock()
+    controller.trendDelta.connect(delta_seen)
+
+    frame = Frame(seq=1, time=102.5, values=[10.0, 20.0, 30.0])
+    controller._on_live_frame(frame)
+
+    payload = json.loads(delta_seen.call_args[0][0])
+    assert len(payload) == 1
+    elapsed, avg = payload[0]
+    assert elapsed == pytest.approx(2.5)
+    assert avg == pytest.approx(20.0)