Polish: live OFA age warning, puppy sorting, responsive fixes, form hints

- HealthRecordForm shows a live amber warning under Test Date when the dog is
  under the OFA minimum certification age (submit-time block unchanged)
- LitterDetail puppies sortable by name / sex / birth date
- Responsive at 375px: DogDetail photos+info grid stacks, header wraps;
  puppy grid uses min(220px,100%); navbar wraps with scrollable icon row;
  calendar uses minmax(0,1fr) columns so cells shrink instead of overflowing
- LitterForm explains why sire/dam selects are locked when editing
- Add .claude/launch.json for the vite dev server

Verified in-browser at 375px and desktop: no horizontal overflow on any page.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

client/src/components/LitterForm.jsx

@@ -116,6 +116,11 @@ function LitterForm({ litter, prefill, onClose, onSave }) {
                   <option key={d.id} value={d.id}>{d.name} {d.registration_number ? `(${d.registration_number})` : ''}</option>
                 ))}
               </select>
+              {!!litter && (
+                <p style={{ fontSize: '0.78rem', color: 'var(--text-muted)', marginTop: '0.25rem' }}>
+                  Parents can't be changed after the litter is created.
+                </p>
+              )}
             </div>
 
             <div className="form-group">