feat: swipe day picker between weeks

app/(tabs)/index.tsx

@@ -257,7 +257,14 @@ export default function TodayScreen() {
           }}
         />
       ) : (
-        <WeekStrip days={visibleDays} selectedDateKey={selectedDateKey} todayDateKey={todayKey} onSelect={setActiveDate} style={styles.weekStrip} />
+        <WeekStrip
+          days={visibleDays}
+          selectedDateKey={selectedDateKey}
+          todayDateKey={todayKey}
+          onSelect={setActiveDate}
+          onSwipeWeek={(direction) => setActiveDate((current) => addDays(current, direction * 7))}
+          style={styles.weekStrip}
+        />
       )}
       <Pressable
         accessibilityRole="button"

app/(tabs)/timetable.tsx

@@ -100,7 +100,14 @@ export default function TimetableScreen() {
         <IconButton icon="chevron-forward" label="Next week" tone="ghost" onPress={() => moveWeek(1)} />
       </View>
     </View>
-    <WeekStrip days={weekDays} selectedDateKey={selectedDateKey} todayDateKey={todayKey} onSelect={setActiveDate} style={styles.weekStrip} />
+    <WeekStrip
+      days={weekDays}
+      selectedDateKey={selectedDateKey}
+      todayDateKey={todayKey}
+      onSelect={setActiveDate}
+      onSwipeWeek={(direction) => setActiveDate((current) => addDays(current, direction * 7))}
+      style={styles.weekStrip}
+    />
 
     <View style={styles.sectionHeader}>
       <View style={styles.sectionCopy}>

components/ui/week-strip.tsx

@@ -1,5 +1,6 @@
 import * as Haptics from 'expo-haptics';
-import { Platform, Pressable, StyleSheet, View, type StyleProp, type ViewStyle } from 'react-native';
+import { useMemo } from 'react';
+import { PanResponder, Platform, Pressable, StyleSheet, View, type StyleProp, type ViewStyle } from 'react-native';
 import { AppText } from './app-text';
 import { colors, radius, spacing } from './tokens';
 import { formatDayHeading, formatWeekdayShort } from '@/lib/date';
@@ -10,6 +11,7 @@ type Props = {
   selectedDateKey: string;
   onSelect: (date: Date) => void;
   todayDateKey?: string;
+  onSwipeWeek?: (direction: -1 | 1) => void;
   style?: StyleProp<ViewStyle>;
   accessibilityLabel?: string;
 };
@@ -18,8 +20,17 @@ const dateKey = (date: Date) => `${date.getFullYear()}-${String(date.getMonth()
 const markerColor = { none: 'transparent', success: colors.semantic.success.solid, warning: colors.semantic.warning.solid, danger: colors.semantic.danger.solid, neutral: colors.neutral.textMuted } as const;
 
 /** The shared selected-date control: coral selection, cobalt today signal, semantic status dot. */
-export function WeekStrip({ days, selectedDateKey, onSelect, todayDateKey, style, accessibilityLabel = 'Choose a day' }: Props) {
-  return <View accessibilityLabel={accessibilityLabel} style={[styles.strip, style]}>
+export function WeekStrip({ days, selectedDateKey, onSelect, todayDateKey, onSwipeWeek, style, accessibilityLabel = 'Choose a day' }: Props) {
+  const panResponder = useMemo(() => PanResponder.create({
+    onMoveShouldSetPanResponderCapture: (_, gestureState) => Boolean(onSwipeWeek) && Math.abs(gestureState.dx) > 24 && Math.abs(gestureState.dx) > Math.abs(gestureState.dy) * 1.2,
+    onPanResponderRelease: (_, gestureState) => {
+      if (!onSwipeWeek || Math.abs(gestureState.dx) < 48 || Math.abs(gestureState.dx) <= Math.abs(gestureState.dy)) return;
+      if (Platform.OS !== 'web') void Haptics.selectionAsync();
+      onSwipeWeek(gestureState.dx < 0 ? 1 : -1);
+    },
+  }), [onSwipeWeek]);
+
+  return <View accessibilityLabel={accessibilityLabel} {...panResponder.panHandlers} style={[styles.strip, style]}>
     {days.map(({ date, disabled = false, marker = 'none' }) => {
       const key = dateKey(date);
       const selected = key === selectedDateKey;