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

backend/local_settings.py

@@ -7,6 +7,7 @@ from pathlib import Path
 class LocalSettings:
     # ===== Defaults =====
     def __init__(self):
+        # Configuration settings
         self.chamber_id = ""
         self.reverse_z_wafer = False
         self.master = {}  # Dict[str, str]
@@ -18,6 +19,16 @@ class LocalSettings:
         self.wafer_detect_timeout = 5000
         self.split_threshold = 40.0
 
+        # Status persistence (operational state)
+        self.connection_status = "Disconnected"
+        self.selected_port = ""
+        self.last_wafer_info = {}  # Dict[str, Any]
+        self.save_data_dir = ""
+        self.activity_log = []  # List[str]
+        self.data_row_count = 0
+        self.data_col_count = 0
+        self.last_csv_path = ""
+
     # ===== File Path Helpers =====
     @classmethod
     def _settings_path(cls, directory: str) -> Path: