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.

src/pygui/backend/controllers/session_controller.py

@@ -12,7 +12,6 @@ from pygui.backend.cluster_average import average_clusters, group_sensors_by_rad
 from pygui.backend.data.csv_recorder import CsvRecorder
 from pygui.backend.models.frame import Frame
 from pygui.backend.models.frame_player import FramePlayer, frames_from_wafer_data
-from pygui.backend.models.replay_stats import ReplayStatsTracker
 from pygui.backend.models.sensor_editor import SensorEditor
 from pygui.backend.models.session_model import SessionModel, SessionUpdate
 from pygui.backend.models.threshold_classifier import ThresholdConfig
@@ -39,7 +38,8 @@ class SessionController(QObject):
     clusterAveragingEnabledChanged = Signal()
     liveStatsChanged = Signal()  # emitted when receivedCount or errorCount change
     # trend: per-frame avg for live graph
-    trendData = Signal(str)  # JSON array of floats
+    trendDelta = Signal(str)  # JSON [[elapsed_s, avg]] — one new point per live frame
+    trendReset = Signal()  # live trend buffer cleared (new stream started)
     # NOTE: dict (QVariantMap), not object — Signal(object) delivers Python
     # dicts to QML as an opaque empty wrapper with no accessible fields.
     comparisonResult = Signal(dict)  # dict with success, distance, warping_path, max_sensor_deviation, series_a, series_b
@@ -59,13 +59,7 @@ class SessionController(QObject):
         self._sensors: list[Sensor] = []
         self._last: Optional[SessionUpdate] = None
         self._elapsed = 0.0
-        self._trend_buffer: list[float] = [] # rolling window
-        self._trend_timestamps: list[float] = []  # monotonic timestamps
-
-        # Trend refresh timer - update every 1s
-        self._trend_timer = QTimer(self)
-        self._trend_timer.setInterval(1000)
-        self._trend_timer.timeout.connect(self._flush_trend)
+        self._stream_start_time: float = 0.0
 
         self._play_timer = QTimer(self)
         self._play_timer.timeout.connect(self._advance)
@@ -85,7 +79,6 @@ class SessionController(QObject):
         self._loaded_file: str = ""
         self._cluster_averaging_enabled = False
         self._active_clusters: list[list[int]] = []
-        self._stats_tracker = ReplayStatsTracker()
         self._received_count: int = 0
         self._error_count: int = 0
 
@@ -293,15 +286,10 @@ class SessionController(QObject):
             self._active_clusters = group_sensors_by_radius(self._sensors)
         self._player.load(frames)
         self._model.reset()
-        self._stats_tracker.reset()
         self._loaded_file = file_path
         self.loadedFileChanged.emit()
         self.sensorsChanged.emit()
         self._emit_current()
-        # Populate stats tracker from all loaded frames for trend chart (P3.1)
-        for frame in self._player._frames:
-            self._stats_tracker.track(frame.seq, frame.values)
-        self.trendData.emit(json.dumps(self._stats_tracker.get_trend()))
 
     @Slot()
     @slot_error_boundary
@@ -309,7 +297,6 @@ class SessionController(QObject):
         """Clear the loaded file, resetting the player and frame states."""
         self._player.load([])
         self._model.reset()
-        self._stats_tracker.reset()
         self._loaded_file = ""
         self.loadedFileChanged.emit()
         self.sensorsChanged.emit()
@@ -689,10 +676,7 @@ class SessionController(QObject):
 
         # Clear out any old data from the prev sessions
         self._model.reset()
-        self._trend_buffer.clear()
-        self._trend_timestamps.clear()
-        self._trend_timer.start()
-        self._stats_tracker.reset()
+        self._reset_live_trend()
         self._last = None
         self._last_raw_frame = None
         self._received_count = 0
@@ -734,7 +718,6 @@ class SessionController(QObject):
     @slot_error_boundary
     def stopStream(self) -> None:
         self._repaint_timer.stop()
-        self._trend_timer.stop()
         self._received_count = 0
         self._error_count = 0
         self.liveStatsChanged.emit()
@@ -760,10 +743,8 @@ class SessionController(QObject):
     @Slot(object)
     @slot_error_boundary
     def _on_live_frame(self, frame: Frame) -> None:
-        import json
         self._received_count += 1
         self.liveStatsChanged.emit()
-        self._stats_tracker.track(frame.seq, frame.values)
         # Main thread (queued). Record raw, process edited; mark dirty for repaint.
         self._last_raw_frame = frame
         edited = Frame(seq=frame.seq, time=frame.time,
@@ -772,22 +753,11 @@ class SessionController(QObject):
         if self._recorder.is_recording:
             self._recorder.write(frame)   # always record raw values, never edited
         self._dirty = True
-        self.trendData.emit(json.dumps(self._stats_tracker.get_trend()))
 
         if self._last and self._last.stats:
             avg = self._last.stats.avg
-            now = time.monotonic()
-            self._trend_buffer.append(avg)
-            self._trend_timestamps.append(now)
-
-            # drop entries older than 60 secs
-            cutoff = now -60
-            while self._trend_timestamps and self._trend_timestamps[0] < cutoff:
-                self._trend_timestamps.pop(0)
-                self._trend_buffer.pop(0)
-
-
-
+            elapsed = time.monotonic() - self._stream_start_time
+            self.trendDelta.emit(json.dumps([[elapsed, avg]]))
 
     def _flush_repaint(self) -> None:
         if not self._dirty:
@@ -843,7 +813,8 @@ class SessionController(QObject):
         self._sensor_editor.clear()
         self._reprocess_current()
 
-    def _flush_trend(self) -> None:
-        import json
-        self.trendData.emit(json.dumps(self._trend_buffer))
+    def _reset_live_trend(self) -> None:
+        """Mark a fresh stream start for elapsed-time trend deltas."""
+        self._stream_start_time = time.monotonic()
+        self.trendReset.emit()