feat: add Dashboard with latest card and weight chart

src/components/LatestMeasurementCard.tsx

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+import React from 'react'
+import { View, Text, StyleSheet } from 'react-native'
+import { Measurement } from '../types'
+
+type Props = { measurement: Measurement | null }
+
+const rows: { label: string; key: keyof Measurement; suffix: string }[] = [
+  { label: 'Gewicht', key: 'weight', suffix: 'kg' },
+  { label: 'BMI', key: 'bmi', suffix: '' },
+  { label: 'Vetpercentage', key: 'bodyFatPercentage', suffix: '%' },
+  { label: 'Vetmassa', key: 'fatMass', suffix: 'kg' },
+  { label: 'Spierpercentage', key: 'musclePercentage', suffix: '%' },
+  { label: 'Spiermassa', key: 'muscleMass', suffix: 'kg' },
+  { label: 'Buikvet', key: 'visceralFat', suffix: '' },
+  { label: 'Stofwisseling', key: 'bmr', suffix: 'kcal' },
+]
+
+export default function LatestMeasurementCard({ measurement }: Props) {
+  if (!measurement) {
+    return (
+      <View style={styles.card}>
+        <Text style={styles.emptyText}>Nog geen metingen</Text>
+      </View>
+    )
+  }
+
+  return (
+    <View style={styles.card}>
+      <Text style={styles.title}>Laatste meting</Text>
+      <Text style={styles.date}>{new Date(measurement.measuredAt).toLocaleDateString('nl-NL')}</Text>
+      {rows.map(r => (
+        <View key={r.key} style={styles.row}>
+          <Text style={styles.rowLabel}>{r.label}</Text>
+          <Text style={styles.rowValue}>
+            {typeof measurement[r.key] === 'number'
+              ? (measurement[r.key] as number).toFixed(1)
+              : measurement[r.key]}{' '}
+            {r.suffix}
+          </Text>
+        </View>
+      ))}
+    </View>
+  )
+}
+
+const styles = StyleSheet.create({
+  card: { backgroundColor: '#fff', borderRadius: 12, padding: 16, margin: 16, shadowColor: '#000', shadowOpacity: 0.1, shadowRadius: 8, elevation: 3 },
+  title: { fontSize: 18, fontWeight: '700', marginBottom: 4 },
+  date: { fontSize: 14, color: '#666', marginBottom: 12 },
+  row: { flexDirection: 'row', justifyContent: 'space-between', paddingVertical: 4 },
+  rowLabel: { fontSize: 14, color: '#555' },
+  rowValue: { fontSize: 14, fontWeight: '600' },
+  emptyText: { fontSize: 16, color: '#999', textAlign: 'center', padding: 20 },
+})

src/components/WeightChart.tsx

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+import React from 'react'
+import { View, Text, StyleSheet, Dimensions } from 'react-native'
+import { LineChart } from 'react-native-chart-kit'
+import { Measurement } from '../types'
+
+type Props = { measurements: Measurement[] }
+
+export default function WeightChart({ measurements }: Props) {
+  if (measurements.length < 2) {
+    return null
+  }
+
+  const sorted = [...measurements].sort(
+    (a, b) => new Date(a.measuredAt).getTime() - new Date(b.measuredAt).getTime()
+  )
+
+  const labels = sorted.map(m => {
+    const d = new Date(m.measuredAt)
+    return `${d.getDate()}/${d.getMonth() + 1}`
+  })
+  const data = sorted.map(m => m.weight)
+
+  return (
+    <View style={styles.container}>
+      <Text style={styles.title}>Gewichtsgrafiek</Text>
+      <LineChart
+        data={{
+          labels: labels.length > 10 ? labels.filter((_, i) => i % Math.ceil(labels.length / 10) === 0) : labels,
+          datasets: [{ data }],
+        }}
+        width={Dimensions.get('window').width - 32}
+        height={220}
+        yAxisSuffix=" kg"
+        chartConfig={{
+          backgroundColor: '#ffffff',
+          backgroundGradientFrom: '#ffffff',
+          backgroundGradientTo: '#ffffff',
+          decimalCount: 1,
+          color: (opacity = 1) => `rgba(76, 175, 80, ${opacity})`,
+          labelColor: () => '#666',
+        }}
+        bezier
+        style={styles.chart}
+      />
+    </View>
+  )
+}
+
+const styles = StyleSheet.create({
+  container: { marginHorizontal: 16, marginBottom: 16 },
+  title: { fontSize: 18, fontWeight: '700', marginBottom: 8 },
+  chart: { borderRadius: 12 },
+})

src/screens/DashboardScreen.tsx

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+import React, { useCallback, useState } from 'react'
+import { View, ScrollView, TouchableOpacity, Text, StyleSheet } from 'react-native'
+import { useFocusEffect } from '@react-navigation/native'
+import { initDatabase, getAllMeasurements, getLatestMeasurement } from '../database/db'
+import { Measurement } from '../types'
+import LatestMeasurementCard from '../components/LatestMeasurementCard'
+import WeightChart from '../components/WeightChart'
+
+type Props = { navigation: any }
+
+export default function DashboardScreen({ navigation }: Props) {
+  const [latest, setLatest] = useState<Measurement | null>(null)
+  const [all, setAll] = useState<Measurement[]>([])
+
+  useFocusEffect(
+    useCallback(() => {
+      const load = async () => {
+        await initDatabase()
+        const allM = await getAllMeasurements()
+        setAll(allM)
+        const latestM = await getLatestMeasurement()
+        setLatest(latestM)
+      }
+      load()
+    }, [])
+  )
+
+  return (
+    <ScrollView style={styles.container}>
+      <LatestMeasurementCard measurement={latest} />
+      <WeightChart measurements={all} />
+
+      <TouchableOpacity style={styles.fab} onPress={() => navigation.navigate('NewMeasurement')}>
+        <Text style={styles.fabText}>+ Nieuwe meting</Text>
+      </TouchableOpacity>
+    </ScrollView>
+  )
+}
+
+const styles = StyleSheet.create({
+  container: { flex: 1, backgroundColor: '#f5f5f5' },
+  fab: { backgroundColor: '#4CAF50', padding: 16, borderRadius: 8, margin: 16, alignItems: 'center' },
+  fabText: { color: '#fff', fontSize: 16, fontWeight: '700' },
+})