Fixing the 10-Second Walk Button Delay

When users tapped "Start Walk," nothing happened for 10 seconds. No spinner, no feedback -- just a frozen button. Then the tracking screen appeared. The flow was:

User taps "Start Walk"
  1. requestPermissions()              ~1-2s
  2. Alert.alert() for background      BLOCKING (waits for tap)
  3. getCurrentLocation(high accuracy)  5-10 SECONDS
  4. createWalkSession()               ~100ms
  5. startBackgroundTracking()         ~500ms
  UI finally transitions

The main culprit: getCurrentLocation() with high accuracy waits for a precise GPS lock, which takes 5-10 seconds if GPS hasn't been used recently.

Fix 1: Fast Location First

// BEFORE: wait for precise GPS (5-10 seconds)
const initialLocation = await getCurrentLocation();

// AFTER: low-accuracy for instant response (~500ms)
const initialLocation = await getCurrentLocation(true);  // fast mode

Low accuracy is fine for centering the map. Background location tracking (started immediately after) delivers high-accuracy updates within seconds.

Fix 2: Non-Blocking Alert

// BEFORE: alert blocks the entire flow
if (!permissions.backgroundLocation) {
  Alert.alert('Background Location Required', ...);  // BLOCKING
}

// AFTER: show alert after UI transition
const shouldShowAlert = !permissions.backgroundLocation;
// ... start session, transition UI ...
if (shouldShowAlert) {
  setTimeout(() => Alert.alert('Background Location Required', ...), 500);
}

Fix 3: Loading Feedback

const [isStartingWalk, setIsStartingWalk] = useState(false);

<TouchableOpacity
  style={[styles.startButton, isStartingWalk && styles.startButtonDisabled]}
  onPress={handleStartWalk}
  disabled={isStartingWalk}
>
  {isStartingWalk ? (
    <ActivityIndicator color="#fff" size="small" />
  ) : (
    <><Ionicons name="walk" size={24} color="#fff" /><Text>Start Walk</Text></>
  )}
</TouchableOpacity>

Result

Same fix applied to "End Walk" -- no need to wait for a precise GPS lock when the walk was already tracked with high-accuracy background updates the entire time.