Pre-visualize the estimated Sud course in the Automatic tab

Adds a static forecast plot to the (previously empty) Automatic tab,
showing the planned temperature course derived from a schedule's
declared ramp rates and hold durations alone (no plant/controller
model - just how long the schedule itself says each step takes).

The client now requests the schedule via Download right after
connecting, routing the reply to the forecast instead of a save
dialog since sud_download_path is only set for the user-initiated
download. SudTask also echoes the just-applied document back after a
successful Upload, so editing the schedule refreshes the forecast
without an extra round trip.

client/brewpi.ui

@@ -705,6 +705,18 @@
      <attribute name="title">
       <string>Automatic</string>
      </attribute>
+     <layout class="QVBoxLayout" name="verticalLayout_forecast">
+      <item>
+       <widget class="QWidget" name="widget_plot_forecast" native="true">
+        <property name="minimumSize">
+         <size>
+          <width>0</width>
+          <height>400</height>
+         </size>
+        </property>
+       </widget>
+      </item>
+     </layout>
     </widget>
     <widget class="QWidget" name="tab_2">
      <attribute name="title">