gui_client: persist connection settings and fix plot history depth

- Save host/port to plot_settings.json on connect; restore on startup
- Raise MAX_PLOT_POINTS from 200 to 2880 so 24 h of data is retained
  even at 30 s polling intervals

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

gui_client.py

@@ -34,7 +34,7 @@ import pyqtgraph as pg
 pg.setConfigOption("background", "#12121e")
 pg.setConfigOption("foreground", "#aaaacc")
 
-MAX_PLOT_POINTS  = 200
+MAX_PLOT_POINTS  = 2880  # 24 h at 30 s polling interval
 
 DARK_STYLE = """
 QWidget                        { background:#1a1a2e; color:#aaaacc; font-size:12px; }
@@ -198,6 +198,7 @@ class ConnectorTab(QWidget):
         self._port = QSpinBox()
         self._port.setRange(1, 65535)
         self._port.setValue(9999)
+        self._load_conn_settings()
         form.addRow("Host:", self._host)
         form.addRow("Port:", self._port)
 
@@ -217,10 +218,35 @@ class ConnectorTab(QWidget):
 
     def _toggle(self):
         if self._btn.text() == "Connect":
+            self._save_conn_settings()
             self.connect_requested.emit(self._host.text(), self._port.value())
         else:
             self.disconnect_requested.emit()
 
+    def _save_conn_settings(self):
+        try:
+            _SETTINGS_PATH.parent.mkdir(parents=True, exist_ok=True)
+            data = {}
+            try:
+                data = json.loads(_SETTINGS_PATH.read_text())
+            except (OSError, json.JSONDecodeError):
+                pass
+            data["host"] = self._host.text()
+            data["port"] = self._port.value()
+            _SETTINGS_PATH.write_text(json.dumps(data, indent=2))
+        except OSError:
+            pass
+
+    def _load_conn_settings(self):
+        try:
+            data = json.loads(_SETTINGS_PATH.read_text())
+            if "host" in data:
+                self._host.setText(data["host"])
+            if "port" in data:
+                self._port.setValue(int(data["port"]))
+        except (OSError, json.JSONDecodeError, KeyError, ValueError):
+            pass
+
     def set_connected(self, host: str, port: int):
         self._btn.setText("Disconnect")
         self._host.setEnabled(False)