feat: add Letzshop frontend for admin and vendor portals

Add complete frontend UI for Letzshop marketplace integration:

Admin portal (/admin/letzshop):
- Vendor overview with Letzshop status cards
- Vendor table with configuration state and sync info
- Configuration modal for API credentials
- Connection testing and manual sync triggers
- Orders modal for viewing vendor orders

Vendor portal (/vendor/{code}/letzshop):
- Orders tab with import, confirm, reject actions
- Settings tab for API credentials management
- Tracking modal for shipment updates
- Order details modal with line items
- Stats display for order status counts

Also includes:
- Routes for both admin and vendor Letzshop pages
- Sidebar navigation updates for both portals
- Alpine.js data functions for reactive UI state

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/routes/admin_pages.py

@@ -538,6 +538,25 @@ async def admin_marketplace_page(
     )
 
 
+@router.get("/letzshop", response_class=HTMLResponse, include_in_schema=False)
+async def admin_letzshop_page(
+    request: Request,
+    current_user: User = Depends(get_current_admin_from_cookie_or_header),
+    db: Session = Depends(get_db),
+):
+    """
+    Render Letzshop management page.
+    Admin overview of Letzshop integration for all vendors.
+    """
+    return templates.TemplateResponse(
+        "admin/letzshop.html",
+        {
+            "request": request,
+            "user": current_user,
+        },
+    )
+
+
 # ============================================================================
 # PRODUCT CATALOG ROUTES
 # ============================================================================

app/routes/vendor_pages.py

@@ -273,6 +273,33 @@ async def vendor_marketplace_page(
     )
 
 
+# ============================================================================
+# LETZSHOP INTEGRATION
+# ============================================================================
+
+
+@router.get(
+    "/{vendor_code}/letzshop", response_class=HTMLResponse, include_in_schema=False
+)
+async def vendor_letzshop_page(
+    request: Request,
+    vendor_code: str = Path(..., description="Vendor code"),
+    current_user: User = Depends(get_current_vendor_from_cookie_or_header),
+):
+    """
+    Render Letzshop integration page.
+    JavaScript loads orders, credentials status, and handles fulfillment operations.
+    """
+    return templates.TemplateResponse(
+        "vendor/letzshop.html",
+        {
+            "request": request,
+            "user": current_user,
+            "vendor_code": vendor_code,
+        },
+    )
+
+
 # ============================================================================
 # TEAM MANAGEMENT
 # ============================================================================