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/DIRECTOR-SHARING.md

@@ -1,6 +1,6 @@
 # Director authoring and file sharing
 
-Open Scenes and select a scene and shot. Existing capture, update, playback and
+Open Authoring and select a scene and shot. Existing capture, update, playback and
 whole-project export controls remain available. Authored scene content, source
 links, assets and contributor credit are preserved.