Re-record the manual on the keyboard layout, and stop the zoom caption promising blocks

Every scene was recorded again on a build of this branch rebased onto the
keyboard work and TD-1, since nearly every scene depends on files those
changed: the develop top bar now carries a star strip and Pick/Reject, the
roll shows flags and stars, and the grid's selection bar gains Label and
Flag. `--changed` could not be trusted to find them, because the rebase
made each picture's commit newer than the sources it was recorded from.

The develop-zoom caption said the wheel goes on "until the pixels are
blocks". On Xvfb the deepest frames come out smooth even though the app
draws past 1:1 nearest-neighbour on a real display (confirmed by eye on
the desktop), and a GIF shrunk to 960 wide could not show 3-pixel blocks
anyway. The caption now says what the clip shows; the prose above it,
which describes what the app does, stays.

tools/manual/scenes.py

@@ -768,8 +768,10 @@ def develop_light():
 
 @scene(media=['develop-zoom.gif'], sources=DEVELOP_SRC + ['ui/dr-ui/src/develop/render.rs'])
 def develop_zoom():
-    """1:1 with a double-click, a pan, and then on in with the wheel until
-    the file's own pixels are hard-edged blocks — which is where it ends."""
+    """1:1 with a double-click, a pan, and then further in with the wheel.
+    Recorded on Xvfb, the deepest frames come out smooth although the app
+    draws past 1:1 with nearest-neighbour on a real display; until that is
+    understood, this scene does not claim to show the blocks."""
     at_develop()
     a = dr.photo(0.62, 0.52)         # the fire escape and the air conditioner
     rec('develop-zoom')