The tutorial intro and "next steps" pages were plain headings with no
send-off. Bookend each tutorial with Angie: a greeting pose welcoming
learners on the intro page, and a superhero pose congratulating them on
the completion page, each beside a speech bubble.
The bubble treatment from the 404 page lived inside the not-found
component, so it's extracted into a reusable docs-content style
(docs-tutorial-mascot) usable from tutorial markdown, and applied to the
intro and completion pages of the Learn Angular, Signals, and Signal
Forms tutorials.
Kam