refactor: update schemas for company-vendor architecture

- Update VendorResponse to use company_id instead of owner fields
- Add VendorDetailResponse with company info (name, email, phone, website)
- Update VendorCreate to require company_id
- Add owner_email, owner_username, vendors list to CompanyDetailResponse
- Remove obsolete VendorTransferOwnership schemas

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

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

models/schema/company.py

@@ -5,6 +5,9 @@ Pydantic schemas for Company model.
 These schemas are used for API request/response validation and serialization.
 """
 
+from datetime import datetime
+from typing import Any
+
 from pydantic import BaseModel, ConfigDict, EmailStr, Field, field_validator
 
 
@@ -106,16 +109,24 @@ class CompanyResponse(BaseModel):
 
 class CompanyDetailResponse(CompanyResponse):
     """
-    Detailed company response including vendor count.
+    Detailed company response including vendor count and owner details.
 
     Used for company detail pages and admin views.
     """
 
+    # Owner details (from related User)
+    owner_email: str | None = Field(None, description="Owner's email address")
+    owner_username: str | None = Field(None, description="Owner's username")
+
+    # Vendor statistics
     vendor_count: int = Field(0, description="Number of vendors under this company")
     active_vendor_count: int = Field(
         0, description="Number of active vendors under this company"
     )
 
+    # Vendors list (optional, for detail view)
+    vendors: list | None = Field(None, description="List of vendors under this company")
+
 
 class CompanyListResponse(BaseModel):
     """Schema for paginated company list."""
@@ -153,3 +164,53 @@ class CompanySummary(BaseModel):
     is_active: bool
     is_verified: bool
     vendor_count: int = 0
+
+
+class CompanyTransferOwnership(BaseModel):
+    """
+    Schema for transferring company ownership to another user.
+
+    This is a critical operation that requires:
+    - Confirmation flag
+    - Reason for audit trail (optional)
+    """
+
+    new_owner_user_id: int = Field(
+        ..., description="ID of the user who will become the new owner", gt=0
+    )
+
+    confirm_transfer: bool = Field(
+        ..., description="Must be true to confirm ownership transfer"
+    )
+
+    transfer_reason: str | None = Field(
+        None,
+        max_length=500,
+        description="Reason for ownership transfer (for audit logs)",
+    )
+
+    @field_validator("confirm_transfer")
+    @classmethod
+    def validate_confirmation(cls, v):
+        """Ensure confirmation is explicitly true."""
+        if not v:
+            raise ValueError("Ownership transfer requires explicit confirmation")
+        return v
+
+
+class CompanyTransferOwnershipResponse(BaseModel):
+    """Response after successful ownership transfer."""
+
+    message: str
+    company_id: int
+    company_name: str
+
+    old_owner: dict[str, Any] = Field(
+        ..., description="Information about the previous owner"
+    )
+    new_owner: dict[str, Any] = Field(
+        ..., description="Information about the new owner"
+    )
+
+    transferred_at: datetime
+    transfer_reason: str | None