Add WellNuo logo to Dashboard header

Replaced "Dashboard" text with app logo image in header:
- Import Image component from react-native
- Replace Text with Image (icon.png) in both header states
- Add logo style: 36x36px with horizontal margins
- Remove unused headerTitle and headerTitleWithBack styles
- Refresh button now uses marginLeft: 'auto' for proper spacing

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/(tabs)/dashboard.tsx

@@ -1,5 +1,5 @@
 import React, { useState, useRef } from 'react';
-import { View, Text, StyleSheet, ActivityIndicator, TouchableOpacity } from 'react-native';
+import { View, Text, StyleSheet, ActivityIndicator, TouchableOpacity, Image } from 'react-native';
 import { WebView } from 'react-native-webview';
 import { Ionicons } from '@expo/vector-icons';
 import { SafeAreaView } from 'react-native-safe-area-context';
@@ -40,7 +40,11 @@ export default function DashboardScreen() {
     return (
       <SafeAreaView style={styles.container} edges={['top']}>
         <View style={styles.header}>
-          <Text style={styles.headerTitle}> </Text>
+          <Image
+            source={require('@/assets/images/icon.png')}
+            style={styles.logo}
+            resizeMode="contain"
+          />
         </View>
         <FullScreenError message={error} onRetry={handleRefresh} />
       </SafeAreaView>
@@ -56,9 +60,11 @@ export default function DashboardScreen() {
             <Ionicons name="arrow-back" size={24} color={AppColors.textPrimary} />
           </TouchableOpacity>
         )}
-        <Text style={[styles.headerTitle, canGoBack && styles.headerTitleWithBack]}>
-          {/* Empty title - WebView has its own dashboard header */}
-        </Text>
+        <Image
+          source={require('@/assets/images/icon.png')}
+          style={styles.logo}
+          resizeMode="contain"
+        />
         <TouchableOpacity style={styles.refreshButton} onPress={handleRefresh}>
           <Ionicons name="refresh" size={22} color={AppColors.primary} />
         </TouchableOpacity>
@@ -116,17 +122,14 @@ const styles = StyleSheet.create({
     padding: Spacing.xs,
     marginRight: Spacing.sm,
   },
-  headerTitle: {
-    flex: 1,
-    fontSize: FontSizes.xl,
-    fontWeight: '700',
-    color: AppColors.textPrimary,
-  },
-  headerTitleWithBack: {
-    marginLeft: 0,
+  logo: {
+    width: 36,
+    height: 36,
+    marginHorizontal: Spacing.md,
   },
   refreshButton: {
     padding: Spacing.xs,
+    marginLeft: 'auto',
   },
   webViewContainer: {
     flex: 1,