feat(01-01): extract models and move config files to new structure

- Move SpeedUnit enum to config/speed_unit.dart
- Move ColorTheme/ColorThemes classes to config/color_themes.dart
- Extract ProcessedGpsData model from gps_data_manager to models/
- Create OverlayMessage typed class for overlay IPC (replaces raw Maps)
- Create ThemeModel with palette rotation and state management

lib/models/overlay_message.dart

@@ -0,0 +1,113 @@
+/// Typed message class for overlay IPC communication
+/// Replaces unvalidated Map data with type-safe serialization
+class OverlayMessage {
+  final String action;
+  final String? speedText;
+  final String? unitText;
+  final String? headingText;
+  final double? heading;
+  final int? unitIndex;
+  final int? themeIndex;
+  final double? overlayWidth;
+  final double? overlayHeight;
+
+  const OverlayMessage({
+    required this.action,
+    this.speedText,
+    this.unitText,
+    this.headingText,
+    this.heading,
+    this.unitIndex,
+    this.themeIndex,
+    this.overlayWidth,
+    this.overlayHeight,
+  });
+
+  /// Factory constructor for display update messages
+  factory OverlayMessage.updateDisplay({
+    required String speedText,
+    required String unitText,
+    required String headingText,
+    required double heading,
+    required int unitIndex,
+    required int themeIndex,
+    double? overlayWidth,
+    double? overlayHeight,
+  }) {
+    return OverlayMessage(
+      action: 'updateDisplay',
+      speedText: speedText,
+      unitText: unitText,
+      headingText: headingText,
+      heading: heading,
+      unitIndex: unitIndex,
+      themeIndex: themeIndex,
+      overlayWidth: overlayWidth,
+      overlayHeight: overlayHeight,
+    );
+  }
+
+  /// Factory constructor for long press close signal
+  factory OverlayMessage.longPressClose() {
+    return const OverlayMessage(action: 'longPressClose');
+  }
+
+  /// Factory constructor for overlay closed notification
+  factory OverlayMessage.overlayClosed() {
+    return const OverlayMessage(action: 'overlayClosed');
+  }
+
+  /// Serialize to Map for overlay IPC
+  Map<String, dynamic> toMap() {
+    final map = <String, dynamic>{'action': action};
+    if (speedText != null) map['speedText'] = speedText;
+    if (unitText != null) map['unitText'] = unitText;
+    if (headingText != null) map['headingText'] = headingText;
+    if (heading != null) map['heading'] = heading;
+    if (unitIndex != null) map['unitIndex'] = unitIndex;
+    if (themeIndex != null) map['themeIndex'] = themeIndex;
+    if (overlayWidth != null) map['overlayWidth'] = overlayWidth;
+    if (overlayHeight != null) map['overlayHeight'] = overlayHeight;
+    return map;
+  }
+
+  /// Deserialize from Map received via overlay IPC
+  factory OverlayMessage.fromMap(Map<dynamic, dynamic> map) {
+    return OverlayMessage(
+      action: map['action'] as String? ?? 'unknown',
+      speedText: map['speedText'] as String?,
+      unitText: map['unitText'] as String?,
+      headingText: map['headingText'] as String?,
+      heading: (map['heading'] as num?)?.toDouble(),
+      unitIndex: map['unitIndex'] as int?,
+      themeIndex: map['themeIndex'] as int?,
+      overlayWidth: (map['overlayWidth'] as num?)?.toDouble(),
+      overlayHeight: (map['overlayHeight'] as num?)?.toDouble(),
+    );
+  }
+
+  /// Create a copy with updated fields
+  OverlayMessage copyWith({
+    String? action,
+    String? speedText,
+    String? unitText,
+    String? headingText,
+    double? heading,
+    int? unitIndex,
+    int? themeIndex,
+    double? overlayWidth,
+    double? overlayHeight,
+  }) {
+    return OverlayMessage(
+      action: action ?? this.action,
+      speedText: speedText ?? this.speedText,
+      unitText: unitText ?? this.unitText,
+      headingText: headingText ?? this.headingText,
+      heading: heading ?? this.heading,
+      unitIndex: unitIndex ?? this.unitIndex,
+      themeIndex: themeIndex ?? this.themeIndex,
+      overlayWidth: overlayWidth ?? this.overlayWidth,
+      overlayHeight: overlayHeight ?? this.overlayHeight,
+    );
+  }
+}

lib/models/processed_gps_data.dart

@@ -0,0 +1,35 @@
+class ProcessedGpsData {
+  final double speed;           // Raw speed in m/s
+  final double heading;         // Raw heading in degrees
+  final String displaySpeed;    // Formatted speed text (with -- logic)
+  final String displayHeading;  // Formatted heading text
+  final bool isSpeedValid;      // True if from recent GPS
+  final bool isHeadingValid;    // True if from recent GPS
+
+  const ProcessedGpsData({
+    required this.speed,
+    required this.heading,
+    required this.displaySpeed,
+    required this.displayHeading,
+    required this.isSpeedValid,
+    required this.isHeadingValid,
+  });
+
+  ProcessedGpsData copyWith({
+    double? speed,
+    double? heading,
+    String? displaySpeed,
+    String? displayHeading,
+    bool? isSpeedValid,
+    bool? isHeadingValid,
+  }) {
+    return ProcessedGpsData(
+      speed: speed ?? this.speed,
+      heading: heading ?? this.heading,
+      displaySpeed: displaySpeed ?? this.displaySpeed,
+      displayHeading: displayHeading ?? this.displayHeading,
+      isSpeedValid: isSpeedValid ?? this.isSpeedValid,
+      isHeadingValid: isHeadingValid ?? this.isHeadingValid,
+    );
+  }
+}

lib/models/theme_model.dart

@@ -0,0 +1,32 @@
+import '../config/color_themes.dart';
+
+/// Theme model that wraps ColorThemes with rotation and state management.
+/// Holds all possible color palettes via delegation, exposing only the current set.
+class ThemeModel {
+  final int _currentIndex;
+
+  const ThemeModel({int currentIndex = 0}) : _currentIndex = currentIndex;
+
+  /// Get the current active color theme
+  ColorTheme get current => ColorThemes.getTheme(_currentIndex);
+
+  /// Get the name of the current theme
+  String get currentSetName => current.name;
+
+  /// Get the current theme index
+  int get currentIndex => _currentIndex;
+
+  /// Rotate to the next theme (circular)
+  ThemeModel rotate() {
+    return ThemeModel(
+      currentIndex: ColorThemes.getNextThemeIndex(_currentIndex),
+    );
+  }
+
+  /// Create a copy with an updated theme index
+  ThemeModel copyWith({int? currentIndex}) {
+    return ThemeModel(
+      currentIndex: currentIndex ?? _currentIndex,
+    );
+  }
+}