refactor(datamodel): rename ProfileMetadata to Metadata for consistency

Because

- Field naming should be consistent with full_name (no profile_ prefix)
- Both fields are part of UserProfile in protobuf

This commit

- Rename ProfileMetadata to Metadata in Owner struct
- Add explicit column:metadata tag for GORM mapping

Author: xiaofei-du

pkg/datamodel/datamodel.go

@@ -61,7 +61,7 @@ type Owner struct {
 	CookieToken            sql.NullString
 	ProfileAvatar          sql.NullString
 	SocialProfileLinks     datatypes.JSON `gorm:"type:jsonb"`
-	ProfileMetadata        datatypes.JSON `gorm:"type:jsonb"`
+	Metadata               datatypes.JSON `gorm:"type:jsonb"`
 	OnboardingStatus       OnboardingStatus
 	FullName               sql.NullString
 }