multiple updates

- colour theme implemented. ThemeService based global switching for future light detection triggers
- test flipflop service for various fun
- navigator widget class with state switching

pi/ui/lib/screens/dashboard_screen.dart

@@ -1,12 +1,15 @@
 import 'dart:async';
-import 'dart:io';
 import 'dart:math';
 import 'package:flutter/material.dart';
 
-import '../services/config_service.dart';
 import '../services/pi_io.dart';
+import '../theme/app_theme.dart';
+import '../widgets/navigator_widget.dart';
 import '../widgets/stat_box.dart';
 
+// test service for triggers
+import '../services/test_flipflop_service.dart';
+
 /// Main dashboard - displays Pi vitals and placeholder stats
 class DashboardScreen extends StatefulWidget {
   const DashboardScreen({super.key});
@@ -17,6 +20,7 @@ class DashboardScreen extends StatefulWidget {
 
 class _DashboardScreenState extends State<DashboardScreen> {
   final _random = Random();
+  final _navigatorKey = GlobalKey<NavigatorWidgetState>();
   Timer? _timer;
 
   double? _piTemp;
@@ -40,33 +44,24 @@ class _DashboardScreenState extends State<DashboardScreen> {
         _temp = 20 + _random.nextInt(60);
       });
     });
+
+    // DEBUG: flip-flop theme + navigator every 2s
+    TestFlipFlopService.instance.start(navigatorKey: _navigatorKey);
   }
 
   @override
   void dispose() {
     _timer?.cancel();
+    TestFlipFlopService.instance.stop();
     super.dispose();
   }
 
-  /// Build navigator image from filesystem
-  Widget _buildNavigatorImage() {
-    final config = ConfigService.instance;
-    final imagePath = '${config.assetsPath}/navigator/${config.navigator}/default.png';
-
-    return Image.file(
-      File(imagePath),
-      fit: BoxFit.contain,
-      errorBuilder: (context, error, stackTrace) {
-        // Graceful fallback - empty box if image missing
-        return const SizedBox.shrink();
-      },
-    );
-  }
-
   @override
   Widget build(BuildContext context) {
+    final theme = AppTheme.of(context);
+
     return Scaffold(
-      backgroundColor: Colors.black,
+      backgroundColor: theme.background,
       body: Padding(
         padding: const EdgeInsets.all(32),
         child: Row(
@@ -84,20 +79,20 @@ class _DashboardScreenState extends State<DashboardScreen> {
                       Text(
                         'SMART SEROW',
                         style: Theme.of(context).textTheme.titleMedium?.copyWith(
-                          color: Colors.teal,
+                          color: theme.subdued,
                           letterSpacing: 2,
                         ),
                       ),
                       Text(
                         '${_voltage.toStringAsFixed(1)}V',
                         style: Theme.of(context).textTheme.titleMedium?.copyWith(
-                          color: _voltage < 12.0 ? Colors.red : Colors.green,
+                          color: _voltage < 12.0 ? theme.highlight : theme.foreground,
                         ),
                       ),
                     ],
                   ),
 
-                  const SizedBox(height: 48),
+                  const SizedBox(height: 20),
 
                   // Main Pi temperature display
                   Expanded(
@@ -107,17 +102,17 @@ class _DashboardScreenState extends State<DashboardScreen> {
                         children: [
                           Text(
                             _piTemp != null ? _piTemp!.toStringAsFixed(1) : '—',
-                            style: const TextStyle(
-                              fontSize: 180,
+                            style: TextStyle(
+                              fontSize: 250,
                               fontWeight: FontWeight.w200,
-                              color: Colors.white,
+                              color: theme.foreground,
                               height: 1,
                             ),
                           ),
                           Text(
                             'Pi Temp',
                             style: Theme.of(context).textTheme.headlineSmall?.copyWith(
-                              color: Colors.grey,
+                              color: theme.subdued,
                             ),
                           ),
                         ],
@@ -144,7 +139,7 @@ class _DashboardScreenState extends State<DashboardScreen> {
             Expanded(
               flex: 1,
               child: Center(
-                child: _buildNavigatorImage(),
+                child: NavigatorWidget(key: _navigatorKey),
               ),
             ),
           ],

pi/ui/lib/screens/overheat_screen.dart

@@ -5,6 +5,7 @@ import 'package:flutter/material.dart';
 
 import '../services/config_service.dart';
 import '../services/pi_io.dart';
+import '../theme/app_theme.dart';
 
 /// Overheat warning screen with shutdown countdown
 ///
@@ -81,30 +82,31 @@ class _OverheatScreenState extends State<OverheatScreen> {
 
   @override
   Widget build(BuildContext context) {
+    final theme = AppTheme.of(context);
     final threshold = ConfigService.instance.overheatThreshold;
 
     return Scaffold(
-      backgroundColor: Colors.black,
+      backgroundColor: theme.background,
       body: Center(
         child: Column(
           mainAxisAlignment: MainAxisAlignment.center,
           children: [
             // Warning icon
-            const Icon(
+            Icon(
               Icons.warning_amber_rounded,
               size: 100,
-              color: Colors.red,
+              color: theme.highlight,
             ),
 
             const SizedBox(height: 16),
 
             // OVERHEATING text
-            const Text(
+            Text(
               'OVERHEATING',
               style: TextStyle(
                 fontSize: 48,
                 fontWeight: FontWeight.bold,
-                color: Colors.red,
+                color: theme.highlight,
                 letterSpacing: 4,
               ),
             ),
@@ -114,10 +116,10 @@ class _OverheatScreenState extends State<OverheatScreen> {
             // Current temperature
             Text(
               _currentTemp != null ? '${_currentTemp!.toStringAsFixed(1)}°C' : '—',
-              style: const TextStyle(
+              style: TextStyle(
                 fontSize: 120,
                 fontWeight: FontWeight.w200,
-                color: Colors.white,
+                color: theme.foreground,
                 height: 1,
               ),
             ),
@@ -127,9 +129,9 @@ class _OverheatScreenState extends State<OverheatScreen> {
             // Threshold info
             Text(
               'Threshold: ${threshold.toStringAsFixed(0)}°C',
-              style: const TextStyle(
+              style: TextStyle(
                 fontSize: 24,
-                color: Colors.grey,
+                color: theme.subdued,
               ),
             ),
 
@@ -138,9 +140,9 @@ class _OverheatScreenState extends State<OverheatScreen> {
             // Countdown
             Text(
               'Shutdown in $_secondsRemaining s',
-              style: const TextStyle(
+              style: TextStyle(
                 fontSize: 32,
-                color: Colors.orange,
+                color: theme.highlight,
                 fontWeight: FontWeight.w500,
               ),
             ),

pi/ui/lib/screens/splash_screen.dart

@@ -1,5 +1,7 @@
 import 'package:flutter/material.dart';
 
+import '../theme/app_theme.dart';
+
 /// Splash screen - shown during initialization
 class SplashScreen extends StatelessWidget {
   final String status;
@@ -8,8 +10,10 @@ class SplashScreen extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final theme = AppTheme.of(context);
+
     return Scaffold(
-      backgroundColor: Colors.black,
+      backgroundColor: theme.background,
       body: Center(
         child: Column(
           mainAxisAlignment: MainAxisAlignment.center,
@@ -17,13 +21,13 @@ class SplashScreen extends StatelessWidget {
             Icon(
               Icons.terrain,
               size: 120,
-              color: Theme.of(context).colorScheme.primary,
+              color: theme.subdued,
             ),
             const SizedBox(height: 24),
             Text(
               'Smart Serow',
               style: Theme.of(context).textTheme.headlineLarge?.copyWith(
-                color: Colors.white,
+                color: theme.foreground,
                 fontWeight: FontWeight.bold,
               ),
             ),
@@ -31,7 +35,7 @@ class SplashScreen extends StatelessWidget {
             Text(
               status,
               style: Theme.of(context).textTheme.bodyLarge?.copyWith(
-                color: Colors.grey,
+                color: theme.subdued,
               ),
             ),
           ],