feat: add mandatory vendor onboarding wizard

Implement 4-step onboarding flow for new vendors after signup:
- Step 1: Company profile setup
- Step 2: Letzshop API configuration with connection testing
- Step 3: Product & order import CSV URL configuration
- Step 4: Historical order sync with progress bar

Key features:
- Blocks dashboard access until completed
- Step indicators with visual progress
- Resume capability (progress persisted in DB)
- Admin skip capability for support cases

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

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

app/routes/vendor_pages.py

@@ -11,7 +11,8 @@ Authentication failures redirect to /vendor/{vendor_code}/login.
 Routes:
 - GET /vendor/{vendor_code}/             → Redirect to login or dashboard
 - GET /vendor/{vendor_code}/login        → Vendor login page
-- GET /vendor/{vendor_code}/dashboard    → Vendor dashboard
+- GET /vendor/{vendor_code}/onboarding   → Vendor onboarding wizard
+- GET /vendor/{vendor_code}/dashboard    → Vendor dashboard (requires onboarding)
 - GET /vendor/{vendor_code}/products     → Product management
 - GET /vendor/{vendor_code}/orders       → Order management
 - GET /vendor/{vendor_code}/customers    → Customer management
@@ -34,6 +35,7 @@ from app.api.deps import (
     get_db,
 )
 from app.services.content_page_service import content_page_service
+from app.services.onboarding_service import OnboardingService
 from models.database.user import User
 
 logger = logging.getLogger(__name__)
@@ -111,6 +113,44 @@ async def vendor_login_page(
 # ============================================================================
 
 
+@router.get(
+    "/{vendor_code}/onboarding", response_class=HTMLResponse, include_in_schema=False
+)
+async def vendor_onboarding_page(
+    request: Request,
+    vendor_code: str = Path(..., description="Vendor code"),
+    current_user: User = Depends(get_current_vendor_from_cookie_or_header),
+    db: Session = Depends(get_db),
+):
+    """
+    Render vendor onboarding wizard.
+
+    Mandatory 4-step wizard that must be completed before accessing dashboard:
+    1. Company Profile Setup
+    2. Letzshop API Configuration
+    3. Product & Order Import Configuration
+    4. Order Sync (historical import)
+
+    If onboarding is already completed, redirects to dashboard.
+    """
+    # Check if onboarding is completed
+    onboarding_service = OnboardingService(db)
+    if onboarding_service.is_completed(current_user.token_vendor_id):
+        return RedirectResponse(
+            url=f"/vendor/{vendor_code}/dashboard",
+            status_code=302,
+        )
+
+    return templates.TemplateResponse(
+        "vendor/onboarding.html",
+        {
+            "request": request,
+            "user": current_user,
+            "vendor_code": vendor_code,
+        },
+    )
+
+
 @router.get(
     "/{vendor_code}/dashboard", response_class=HTMLResponse, include_in_schema=False
 )
@@ -118,16 +158,27 @@ async def vendor_dashboard_page(
     request: Request,
     vendor_code: str = Path(..., description="Vendor code"),
     current_user: User = Depends(get_current_vendor_from_cookie_or_header),
+    db: Session = Depends(get_db),
 ):
     """
     Render vendor dashboard.
 
+    Redirects to onboarding if not completed.
+
     JavaScript will:
     - Load vendor info via API
     - Load dashboard stats via API
     - Load recent orders via API
     - Handle all interactivity
     """
+    # Check if onboarding is completed
+    onboarding_service = OnboardingService(db)
+    if not onboarding_service.is_completed(current_user.token_vendor_id):
+        return RedirectResponse(
+            url=f"/vendor/{vendor_code}/onboarding",
+            status_code=302,
+        )
+
     return templates.TemplateResponse(
         "vendor/dashboard.html",
         {