Add support for list "random" sorting

## Problem / Opportunity

Search results already support sorting randomly, but lists don't. A shareable link to a randomly-ordered list would be handy for e.g. book clubs that use a list to vote on the next read, where a fixed order biases the selection. Eg [Book Club 2026-08](https://openlibrary.org/people/ScarTissue/lists/OL341354L/Book_Club_2026-08).

## Proposal

Add a "random" option to the list sort control. Selecting it should add a seed as a URL parameter so that a given link always yields the same order, and we can then also offer the shuffle button we already have on other pages to re-roll the seed.

Implementation Details (for maintainers)

#### Related files
* `openlibrary/templates/type/list/view_body.html`
* `openlibrary/plugins/openlibrary/lists.py`
* `openlibrary/templates/search/sort_options.html` — existing random sort + shuffle button

#### Requirements Checklist
* [ ] List pages offer a "random" sort option
* [ ] Selecting random sets a seed URL param, so the same URL reproduces the same order
* [ ] A shuffle button re-rolls the seed

#### Instructions for Contributors
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Start with openlibrary/templates/type/list/view_body.html and compare its sort control with the random sort and shuffle button in openlibrary/templates/search/sort_options.html. Then trace list sorting in openlibrary/plugins/openlibrary/lists.py. Done means list pages offer random sorting, preserve a seed in the URL for repeatable ordering, and provide a shuffle action that changes the seed.

Written by the indexing model from the issue text.