Show the composite in the grid in the manual, and say how it gets there

The panorama scene now ends in the grid, on the composite in its wide
cell beside the twelve frames it was made from, with the thumbnail the
merge made: the picture is taken straight after the merge, before any
rescan could have found the file. The manual's library section says how
a panorama's cell is sized and packed, and its panorama section that the
composite is in the grid the moment it is written. panorama.md §9 records
the race that kept it out, the catalogue-then-register path that
replaced it, how the thumbnail is developed, and the layout's classes.

tools/manual/scenes.py

@@ -1314,9 +1314,10 @@ def join(name, parts):
         os.remove(f'{OUT}/{p}.mp4')
 
 
-@scene(media=['panorama.gif', 'panorama-aligned.png', 'panorama-filled.png'],
+@scene(media=['panorama.gif', 'panorama-aligned.png', 'panorama-filled.png', 'panorama-in-grid.png'],
        sources=COMMON + ['ui/dr-ui/ui/merge.slint', 'ui/dr-ui/src/merge_ui.rs', 'ui/dr-ui/src/merge.rs',
-                         'core/dr-pano/src/**'])
+                         'ui/dr-ui/src/merge_thumbs.rs', 'ui/dr-ui/src/library_ui/layout.rs',
+                         'ui/dr-ui/ui/library.slint', 'core/dr-pano/src/**'])
 def panorama():
     select_pano()
     rec('panorama-0')
@@ -1358,6 +1359,14 @@ def panorama():
     wait_for_new(DEMO_LIBRARY, '.dng', started, 600) if DEMO_LIBRARY else pause(60)
     pause(5)
     at_library()
+    # The composite in the grid beside its frames, in its wide cell, with the
+    # thumbnail the merge made: catalogued when it was written, not when a
+    # scan got round to it.
+    grid_top()
+    dr.wait_for(f'{PANO_FIRST}-pano', 120)
+    show_cell(f'{PANO_FIRST}-pano')
+    pause(2)
+    shot('panorama-in-grid')
 
 
 # --- settings ---------------------------------------------------------------