feat(tenancy): show merchant & store details on merchant user detail page

Add clickable card grids for owned merchants and store memberships,
replacing static count-only banners with linked summaries.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

models/schema/auth.py

@@ -49,6 +49,25 @@ class PlatformSelectResponse(BaseModel):
     platform_code: str
 
 
+class OwnedMerchantSummary(BaseModel):
+    """Summary of a merchant owned by a user."""
+
+    id: int
+    name: str
+    is_active: bool
+    store_count: int
+
+
+class StoreMembershipSummary(BaseModel):
+    """Summary of a user's store membership."""
+
+    store_id: int
+    store_code: str
+    store_name: str
+    user_type: str
+    is_active: bool
+
+
 class UserDetailResponse(UserResponse):
     """Extended user response with additional details."""
 
@@ -58,6 +77,8 @@ class UserDetailResponse(UserResponse):
     is_email_verified: bool = False
     owned_merchants_count: int = 0
     store_memberships_count: int = 0
+    owned_merchants: list[OwnedMerchantSummary] = []
+    store_memberships: list[StoreMembershipSummary] = []
 
 
 class UserUpdate(BaseModel):