fix(journey): emptying the location field in the entry editor removes the location

The field showed the stored place as soon as the search query was empty, so
deleting the last character snapped it back and the location could never be
removed. Clearing the field now empties the place and its coordinates, closes
the suggestions and drops any search answer that comes back afterwards. Typed
text without a picked result keeps the stored location as before. The hook is
shared, so the desktop dialog and the phone sheet both get the fix.

Refs #2615

client/tests/unit/mobile/journey/MJourneyEntrySheet.test.tsx

@@ -1333,3 +1333,24 @@ describe('MJourneyEntrySheet clips', () => {
     expect(document.querySelectorAll('svg.lucide-play')).toHaveLength(1);
   });
 });
+
+// FE-MOB-JENTRY-057: the phone half of the location field that snapped back (#2615).
+
+describe('MJourneyEntrySheet location field', () => {
+  it('FE-MOB-JENTRY-057: emptying the location keeps the field empty, drops the pin and saves no place', async () => {
+    const user = userEvent.setup();
+    const { onSave } = mountSheet(buildEntry({ id: 5, location_name: 'Rome', location_lat: 41.9, location_lng: 12.5 }));
+    const input = screen.getByPlaceholderText('Search location...');
+    expect(input).toHaveValue('Rome');
+    expect(document.querySelector('svg.lucide-map-pin')).toBeInTheDocument();
+
+    fireEvent.change(input, { target: { value: 'Rom' } });
+    fireEvent.change(input, { target: { value: '' } });
+    expect(input).toHaveValue('');
+    expect(document.querySelector('svg.lucide-map-pin')).not.toBeInTheDocument();
+
+    await user.click(screen.getByRole('button', { name: 'Save' }));
+    await waitFor(() => expect(onSave).toHaveBeenCalled());
+    expect(onSave.mock.calls[0][0]).toMatchObject({ location_name: null, location_lat: null, location_lng: null });
+  });
+});