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

server/db/mysql/user_privacy_schema.go

@@ -0,0 +1,64 @@
+//go:build mysql
+// +build mysql
+
+package mysql
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+
+	"github.com/jmoiron/sqlx"
+)
+
+const userPrivacyMigrationLock = "CONCAT('im_user_privacy:', LEFT(SHA2(DATABASE(), 256), 40))"
+
+// ensureUserPrivacySchema adds columns of im_user_privacy_settings that were
+// introduced after the table's initial release. Databases created fresh by
+// createIMUserProductTables already have them; legacy databases are upgraded
+// in place. A missing table is skipped: it is created by the fresh-install
+// path and there is nothing to upgrade yet.
+func ensureUserPrivacySchema(db *sqlx.DB) error {
+	ctx := context.Background()
+	conn, err := db.Connx(ctx)
+	if err != nil {
+		return err
+	}
+	defer conn.Close()
+
+	var locked sql.NullInt64
+	if err = conn.QueryRowContext(ctx, "SELECT GET_LOCK("+userPrivacyMigrationLock+", 60)").Scan(&locked); err != nil {
+		return err
+	}
+	if !locked.Valid || locked.Int64 != 1 {
+		return errors.New("mysql: timed out waiting for user privacy migration lock")
+	}
+	defer conn.ExecContext(ctx, "SELECT RELEASE_LOCK("+userPrivacyMigrationLock+")")
+
+	tableExists, err := identityTableExists(ctx, conn, "im_user_privacy_settings")
+	if err != nil || !tableExists {
+		return err
+	}
+
+	// Column definitions mirror createIMUserProductTables; the SELECT in
+	// userPrivacyByUID references every one of them.
+	columns := []struct{ name, ddl string }{
+		{"profile_visibility", "VARCHAR(32) NOT NULL DEFAULT 'friends'"},
+		{"last_seen_visibility", "VARCHAR(32) NOT NULL DEFAULT 'friends'"},
+		{"read_receipts", "TINYINT NOT NULL DEFAULT 1"},
+		{"friend_request_verification", "TINYINT NOT NULL DEFAULT 1"},
+		{"group_invite_verification", "TINYINT NOT NULL DEFAULT 0"},
+	}
+	for _, col := range columns {
+		exists, err := identityColumnExists(ctx, conn, "im_user_privacy_settings", col.name)
+		if err != nil {
+			return err
+		}
+		if !exists {
+			if _, err = conn.ExecContext(ctx, "ALTER TABLE im_user_privacy_settings ADD COLUMN "+col.name+" "+col.ddl); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}