feat: update API endpoints for company-vendor architecture

- Add transfer-ownership endpoint to companies API
- Add user search endpoint for autocomplete (/admin/users/search)
- Update company detail endpoint to include owner info and vendors list
- Update vendor endpoints to use company relationship for ownership
- Update deps.py vendor access check to use company.owner_user_id

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

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

app/api/v1/admin/users.py

@@ -49,3 +49,38 @@ def get_user_statistics(
 ):
     """Get user statistics for admin dashboard (Admin only)."""
     return stats_service.get_user_statistics(db)
+
+
+@router.get("/search")
+def search_users(
+    q: str = Query(..., min_length=2, description="Search query (username or email)"),
+    limit: int = Query(10, ge=1, le=50),
+    db: Session = Depends(get_db),
+    current_admin: User = Depends(get_current_admin_api),
+):
+    """
+    Search users by username or email (Admin only).
+
+    Used for autocomplete in ownership transfer.
+    """
+    search_term = f"%{q.lower()}%"
+    users = (
+        db.query(User)
+        .filter(
+            (User.username.ilike(search_term)) | (User.email.ilike(search_term))
+        )
+        .limit(limit)
+        .all()
+    )
+
+    return {
+        "users": [
+            {
+                "id": user.id,
+                "username": user.username,
+                "email": user.email,
+                "is_active": user.is_active,
+            }
+            for user in users
+        ]
+    }