fix: auto-provision im_user_privacy_settings columns on startup

Zentao #24/#25: commit 50f8581 added friend_request_verification and group_invite_verification to userPrivacyByUID, but existing databases lack those columns, so GetPrivacy failed with Error 1054 and every cross-user profile/qrcodes/friend-request endpoint returned 500.

Add user_privacy_schema.go which, under GET_LOCK, checks information_schema and ALTERs in any missing privacy columns, wired into the root adapter Open() and per-tenant TenantAdapterFor so tenant-scoped databases are provisioned too.

server/db/mysql/adapter.go

@@ -284,6 +284,9 @@ func (a *adapter) Open(jsonconfig json.RawMessage) error {
 				return errors.New("mysql adapter failed to open tenant registry database: " + err.Error())
 			}
 		}
+		if err = ensureUserPrivacySchema(a.db); err != nil {
+			return errors.New("mysql adapter failed to ensure user privacy schema: " + err.Error())
+		}
 	}
 	return err
 }
@@ -494,6 +497,10 @@ func (a *adapter) TenantAdapterFor(tenantID t.TenantID) (dbadapter.TenantBusines
 		db.Close()
 		return nil, nil, err
 	}
+	if err = ensureUserPrivacySchema(db); err != nil {
+		db.Close()
+		return nil, nil, errors.New("mysql adapter failed to ensure user privacy schema for tenant: " + err.Error())
+	}
 	registryDB := a.registryDB
 	if registryDB == nil {
 		registryDB = a.db