Add SettingsTab, StatusTab, DataTab and wire up DeviceController

- SettingsTab: chamber ID, master CSV mapping (families A-Z), wafer
  behavior toggle, light/dark mode toggle, Edit CSV Metadata dialog
- StatusTab: connection status card, wafer info, activity log (blank
  until Detect Wafer fires from the side rail)
- DataTab: empty state, ready for parsed data
- HomePage: side rail buttons dispatch device actions and jump to
  Status tab; selectedSideActionIndex defaults to -1 on startup
- DeviceController registered as QML context property in main.py
- LocalSettings: added status persistence fields
- Theme: added subheadingColor and disabledText
- Added serialcomm/ package and backend data/graph modules
- gitignore: restore clean version

ISC/Tabs/SettingsTab.qml

@@ -23,8 +23,7 @@ Item {
     }
 
     function handleCsvSelected(filePath) {
-        console.log("Doing work with:", filePath);
-        // @todo: implement CSV metadata handling after file selection.
+        // Selection confirmed — metadata editing is handled inline inside SelectFileDialog.
     }
 
     // ===== Settings Data Helpers =====
@@ -136,7 +135,7 @@ Item {
         title: "Choose Master CSV"
         nameFilters: ["CSV files (*.csv)"]
         property string targetFamily: ""
-        onAccepted: settingsModel.setMaster(targetFamily, selectedFile.toLocalFile())
+        onAccepted: settingsModel.setMaster(targetFamily, String(selectedFile).replace(/^file:\/\//, ""))
     }
 
     // ===== Settings Page Layout =====
@@ -206,7 +205,6 @@ Item {
                             Layout.minimumWidth: Theme.settingsFieldMinWidth
                             placeholderText: "Enter chamber ID"
                             text: settingsModel.chamberId
-                            onEditingFinished: settingsModel.setChamberId(text)
 
                             Connections {
                                 target: settingsModel
@@ -222,7 +220,10 @@ Item {
                             text: "Set"
                             Layout.preferredWidth: 90
                             Layout.preferredHeight: Theme.settingsButtonHeight
-                            onClicked: settingsModel.setChamberId(chamberField.text)
+                            onClicked: {
+                                settingsModel.setChamberId(chamberField.text);
+                                settingsModel.saveSettings();
+                            }
                         }
                     }
                 }
@@ -389,6 +390,11 @@ Item {
                         Layout.fillWidth: true
                     }
                 }
+
+                // Bottom spacer so last group isn't flush with scroll edge
+                Item {
+                    Layout.preferredHeight: Theme.settingsSectionSpacing
+                }
             }
         }
 
@@ -406,7 +412,7 @@ Item {
                 }
                 GradientStop {
                     position: 1.0
-                    color: Qt.transparent
+                    color: Qt.rgba(0, 0, 0, 0)
                 }
             }