MAINT: update `output_scroll` tags to `collapse-##` tags in lectures

[mmcky]

Once #300 is ready -- we should globally migrate these tags in the lecture series.

[mmcky]

Superseded by QuantEcon/project-theme-parity#19, decided 2026-09-29. The lectures do move from output_scroll to a collapse tag, as proposed here, but at the mystmd cutover rather than on this theme. Every output_scroll and scroll-output becomes collapse-output-24, which the mystmd theme renders as the Expand / Collapse bar on the output, at about the height of today's scroll box.

Nothing changes in this theme. As #300 shipped, collapse-N caps only the code input, and the theme's script treats any tag_collapse* class as an input collapser, so a collapse-output-N tag here adds a stray Expand bar under the input and leaves the output at full height. The lecture sources therefore keep their scroll tags until cutover. The rename is tracked in QuantEcon/workspace-lectures#64.

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