Rename the Scenes panel to Authoring and lay it out in steps

The panel reads AUTHORING and groups its controls under SCENE, SHOTS,
PREVIEW and SAVE & SHARE headings, with the EDIT DETAILS / SHARE SCENE
row moved beside EXPORT / IMPORT. Text is larger with more contrast,
shots are numbered, every action has a tooltip and the status line is a
live region. Outside playback, buttons that would do nothing are
disabled. New labels are translated in every shipped language; PLAY
uses its own catalog context apart from the radio's PLAY.

docs/SCENE-DOCUMENT.md

@@ -1,6 +1,6 @@
 # Scene document format
 
-Scenes exports a UTF-8 JSON project. Version 5 adds [data packs](DIRECTOR-DATA-PACKS.md)
+Authoring exports a UTF-8 JSON project. Version 5 adds [data packs](DIRECTOR-DATA-PACKS.md)
 and is the write format. Versions 1, 2, 3, 4 and unversioned legacy files migrate on
 import without converting their existing shots into authored moves. Unknown versions or unsupported fields are rejected with
 a field path before the current project, selection or saved bytes change.