Fix biased random sort by using Fisher-Yates shuffle

[infinitejones]

Summary

• The random sort option used Array.sort() with a random comparator, which is a well-known antipattern that produces biased results — items tend to stay near their original (alphabetically sorted) position
• This is especially noticeable when filenames share a common prefix (e.g. France - beach, France - city, Italy - beach, Italy - city), as the alphabetical pre-sort clusters them and the biased shuffle preserves those clusters
• Replaced with Fisher-Yates shuffle for both media and directories, which guarantees a uniform random permutation
• The existing seeded PRNG is still used, so the shuffle remains deterministic within a page load

Test plan

• Select random sorting on a gallery with many similarly-named files and verify items are well-mixed
• Verify the shuffle is stable within a page load (navigating away and back gives the same order)
• Verify directory random sorting also works correctly

🤖 Generated with Claude Code

[bpatrik]

thanks!