feat(dav): add a room building name to IRoomMetadata

Assisted-by: ClaudeCode:claude-opus-5
Signed-off-by: Rikdekker <Rikdekker@users.noreply.github.com>

Author: Rikdekker

lib/public/Calendar/Room/IRoomMetadata.php

@@ -36,6 +36,17 @@ interface IRoomMetadata {
 	 */
 	public const CAPACITY = '{http://nextcloud.com/ns}room-seating-capacity';
 
+	/**
+	 * The name of the building this room is located in
+	 *
+	 * Clients group rooms by building. Without this key they have to guess a
+	 * building from BUILDING_ADDRESS, which only works for backends that
+	 * happen to put the building name first.
+	 *
+	 * @since 35.0.0
+	 */
+	public const BUILDING_NAME = '{http://nextcloud.com/ns}room-building-name';
+
 	/**
 	 * The physical address of the building this room is located in
 	 *