feat(flow): retry failed orders

Add ability to re-import individual ERROR/SKIPPED orders directly from
the order detail modal. Downloads narrow date range from GoMag API,
finds the specific order, and re-runs import_single_order().

Backend:
- New retry_service.py with retry_single_order() — downloads order_date
  ±1 day from GoMag, finds order by number, imports via import_service
- Guard: blocks retry during active sync (_sync_lock check)
- POST /api/orders/{order_number}/retry endpoint

Frontend:
- "Reimporta" button in modal footer (visible only for ERROR/SKIPPED)
- Spinner during retry, success/error feedback with auto-refresh

Cache-bust: shared.js?v=18

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/app/templates/base.html

@@ -135,6 +135,7 @@
                     <div id="detailError" class="alert alert-danger mt-3" style="display:none;"></div>
                 </div>
                 <div class="modal-footer">
+                    <button type="button" id="detailRetryBtn" class="btn btn-sm btn-outline-primary" style="display:none"><i class="bi bi-arrow-clockwise"></i> Reimporta</button>
                     <button type="button" class="btn btn-secondary" data-bs-dismiss="modal">Inchide</button>
                 </div>
             </div>
@@ -143,7 +144,7 @@
 
     <script>window.ROOT_PATH = "{{ rp }}";</script>
     <script src="https://cdn.jsdelivr.net/npm/bootstrap@5.3.2/dist/js/bootstrap.bundle.min.js"></script>
-    <script src="{{ rp }}/static/js/shared.js?v=17"></script>
+    <script src="{{ rp }}/static/js/shared.js?v=18"></script>
     <script>
     // Dark mode toggle
     function toggleDarkMode() {