docs: put every chapter back in the readme demo gif, and fix an orphaned card

The first version of this gif dropped three chapters, not the one that was
asked for, and it cut in a place that left a title card with nothing behind
it. At 23.4s it showed "Schedule it once, then forget it" and then cut
straight to "Let it fetch the file" — two cards back to back, with the X
chapter's actual content never appearing. Scheduling is a capability worth
showing, and a title with no content reads as broken.

Now only Bumble is removed. The run from 0 to 64.9s is uncut, so no
boundary exists that could orphan a card, and there is a single splice to
the end card.

Fast-forwarded, but not uniformly: the title cards play at normal speed so
they stay readable while the screen content runs at 2.5x. Static frames
cost almost nothing in a gif with diff_mode=rectangle, so holding the cards
is close to free, and pushing the content harder is where the savings are.
That combination is both shorter and smaller than a uniform 1.75x pass over
the same material: 37.9s and 4.97MB versus 39.9s and 6.27MB.

Ends up slightly smaller than the previous three-chapter version while
carrying five chapters, and matches the 37s of the gif it replaced.

Author: esokullu