feat(vendor): add contact info inheritance from company

Vendors can now override company contact information for specific branding.
Fields are nullable - if null, value is inherited from parent company.

Database changes:
- Add vendor.contact_email, contact_phone, website, business_address, tax_number
- All nullable (null = inherit from company)
- Alembic migration: 28d44d503cac

Model changes:
- Add effective_* properties for resolved values
- Add get_contact_info_with_inheritance() helper

Schema changes:
- VendorCreate: Optional contact fields for override at creation
- VendorUpdate: Contact fields + reset_contact_to_company flag
- VendorDetailResponse: Resolved values + *_inherited flags

API changes:
- GET/PUT vendor endpoints return resolved contact info
- PUT accepts contact overrides (empty string = reset to inherit)
- _build_vendor_detail_response helper for consistent responses

Service changes:
- admin_service.update_vendor handles reset_contact_to_company flag
- Empty strings converted to None for inheritance

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

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

app/api/v1/admin/vendors.py

@@ -116,23 +116,14 @@ def get_vendor_statistics_endpoint(
     )
 
 
-@router.get("/{vendor_identifier}", response_model=VendorDetailResponse)
-def get_vendor_details(
-    vendor_identifier: str = Path(..., description="Vendor ID or vendor_code"),
-    db: Session = Depends(get_db),
-    current_admin: User = Depends(get_current_admin_api),
-):
+def _build_vendor_detail_response(vendor) -> VendorDetailResponse:
     """
-    Get detailed vendor information including company and owner details (Admin only).
+    Helper to build VendorDetailResponse with resolved contact info.
 
-    Accepts either vendor ID (integer) or vendor_code (string).
-
-    Returns vendor info with company contact details and owner info.
-
-    Raises:
-        VendorNotFoundException: If vendor not found (404)
+    Contact fields are resolved using vendor override or company fallback.
+    Inheritance flags indicate if value comes from company.
     """
-    vendor = vendor_service.get_vendor_by_identifier(db, vendor_identifier)
+    contact_info = vendor.get_contact_info_with_inheritance()
 
     return VendorDetailResponse(
         # Vendor fields
@@ -151,15 +142,39 @@ def get_vendor_details(
         updated_at=vendor.updated_at,
         # Company info
         company_name=vendor.company.name,
-        company_contact_email=vendor.company.contact_email,
-        company_contact_phone=vendor.company.contact_phone,
-        company_website=vendor.company.website,
         # Owner details (from company)
         owner_email=vendor.company.owner.email,
         owner_username=vendor.company.owner.username,
+        # Resolved contact info with inheritance flags
+        **contact_info,
+        # Original company values for UI reference
+        company_contact_email=vendor.company.contact_email,
+        company_contact_phone=vendor.company.contact_phone,
+        company_website=vendor.company.website,
     )
 
 
+@router.get("/{vendor_identifier}", response_model=VendorDetailResponse)
+def get_vendor_details(
+    vendor_identifier: str = Path(..., description="Vendor ID or vendor_code"),
+    db: Session = Depends(get_db),
+    current_admin: User = Depends(get_current_admin_api),
+):
+    """
+    Get detailed vendor information including company and owner details (Admin only).
+
+    Accepts either vendor ID (integer) or vendor_code (string).
+
+    Returns vendor info with company contact details, owner info, and
+    resolved contact fields (vendor override or company default).
+
+    Raises:
+        VendorNotFoundException: If vendor not found (404)
+    """
+    vendor = vendor_service.get_vendor_by_identifier(db, vendor_identifier)
+    return _build_vendor_detail_response(vendor)
+
+
 @router.put("/{vendor_identifier}", response_model=VendorDetailResponse)
 def update_vendor(
     vendor_identifier: str = Path(..., description="Vendor ID or vendor_code"),
@@ -176,40 +191,18 @@ def update_vendor(
     - Basic info: name, description, subdomain
     - Marketplace URLs
     - Status: is_active, is_verified
+    - Contact info: contact_email, contact_phone, website, business_address, tax_number
+      (these override company defaults; set to empty to reset to inherit)
 
     **Cannot update:**
     - `vendor_code` (immutable)
-    - Business contact info (use company update endpoints)
 
     Raises:
         VendorNotFoundException: If vendor not found (404)
     """
     vendor = vendor_service.get_vendor_by_identifier(db, vendor_identifier)
     vendor = admin_service.update_vendor(db, vendor.id, vendor_update)
-
-    return VendorDetailResponse(
-        id=vendor.id,
-        vendor_code=vendor.vendor_code,
-        subdomain=vendor.subdomain,
-        name=vendor.name,
-        description=vendor.description,
-        company_id=vendor.company_id,
-        letzshop_csv_url_fr=vendor.letzshop_csv_url_fr,
-        letzshop_csv_url_en=vendor.letzshop_csv_url_en,
-        letzshop_csv_url_de=vendor.letzshop_csv_url_de,
-        is_active=vendor.is_active,
-        is_verified=vendor.is_verified,
-        created_at=vendor.created_at,
-        updated_at=vendor.updated_at,
-        # Company info
-        company_name=vendor.company.name,
-        company_contact_email=vendor.company.contact_email,
-        company_contact_phone=vendor.company.contact_phone,
-        company_website=vendor.company.website,
-        # Owner details (from company)
-        owner_email=vendor.company.owner.email,
-        owner_username=vendor.company.owner.username,
-    )
+    return _build_vendor_detail_response(vendor)
 
 
 # NOTE: Ownership transfer is now at the Company level.
@@ -243,29 +236,7 @@ def toggle_vendor_verification(
         db.commit()  # ✅ ARCH: Commit at API level for transaction control
         logger.info(f"Vendor verification updated: {message}")
 
-    return VendorDetailResponse(
-        id=vendor.id,
-        vendor_code=vendor.vendor_code,
-        subdomain=vendor.subdomain,
-        name=vendor.name,
-        description=vendor.description,
-        company_id=vendor.company_id,
-        letzshop_csv_url_fr=vendor.letzshop_csv_url_fr,
-        letzshop_csv_url_en=vendor.letzshop_csv_url_en,
-        letzshop_csv_url_de=vendor.letzshop_csv_url_de,
-        is_active=vendor.is_active,
-        is_verified=vendor.is_verified,
-        created_at=vendor.created_at,
-        updated_at=vendor.updated_at,
-        # Company info
-        company_name=vendor.company.name,
-        company_contact_email=vendor.company.contact_email,
-        company_contact_phone=vendor.company.contact_phone,
-        company_website=vendor.company.website,
-        # Owner details (from company)
-        owner_email=vendor.company.owner.email,
-        owner_username=vendor.company.owner.username,
-    )
+    return _build_vendor_detail_response(vendor)
 
 
 @router.put("/{vendor_identifier}/status", response_model=VendorDetailResponse)
@@ -294,29 +265,7 @@ def toggle_vendor_status(
         db.commit()  # ✅ ARCH: Commit at API level for transaction control
         logger.info(f"Vendor status updated: {message}")
 
-    return VendorDetailResponse(
-        id=vendor.id,
-        vendor_code=vendor.vendor_code,
-        subdomain=vendor.subdomain,
-        name=vendor.name,
-        description=vendor.description,
-        company_id=vendor.company_id,
-        letzshop_csv_url_fr=vendor.letzshop_csv_url_fr,
-        letzshop_csv_url_en=vendor.letzshop_csv_url_en,
-        letzshop_csv_url_de=vendor.letzshop_csv_url_de,
-        is_active=vendor.is_active,
-        is_verified=vendor.is_verified,
-        created_at=vendor.created_at,
-        updated_at=vendor.updated_at,
-        # Company info
-        company_name=vendor.company.name,
-        company_contact_email=vendor.company.contact_email,
-        company_contact_phone=vendor.company.contact_phone,
-        company_website=vendor.company.website,
-        # Owner details (from company)
-        owner_email=vendor.company.owner.email,
-        owner_username=vendor.company.owner.username,
-    )
+    return _build_vendor_detail_response(vendor)
 
 
 @router.delete("/{vendor_identifier}")