Order the difficulty filter from Easy to Hard

[Pandamachi]

The Difficulty select in the lobby's progress panel listed its options as All, Easy, Hard, Medium and now reads All, Easy, Medium, Hard, with the rest of the detail in #281.

The comparator orders by position in LEVELS, which web/problem-picker.js exports and which this module already imports to decide which difficulties it will admit at all. Reusing that array keeps the scale defined once; an order written out in the comparator would be a second copy to keep in step with the picker. The duration menu on the next line already passes a comparator, so this is the shape the helper was written for rather than a parameter added for it.

The existing test "filter options are deduplicated, ordered, and free of unreadable values" used only Easy and Medium, whose alphabetical and scale orders agree, so it passed either way and left the comparator unpinned. The case added beside it passes buildProgressModel three records whose difficulties are Hard, Easy and Medium and asserts options.difficulty is ["Easy", "Medium", "Hard"]. Run against the parent commit it fails with ["Easy", "Hard", "Medium"], which is the reported symptom.

./scripts/test.sh exits 0 on this branch, no lane failed, and the node browser suite reports 1042 tests with 858 passing and 0 failing. make indent is clean and leaves the two changed files as they are.

That run left several lanes unchecked, so they are CI's to confirm rather than mine: 184 node browser tests skipped for want of Playwright Chromium, a built server binary and javac, plus the cargo-audit, actionlint, ruff and shellcheck lanes, and the formatter chain skipped ruff and shfmt. The menu was not watched in a running lobby either; the list is computed in web/progress.js before the page renders it, which is the function the new test calls directly.

Closes #281

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Summary by cubic

Orders the difficulty filter in the lobby's progress panel by the game's level scale instead of alphabetically, so the menu now shows All, Easy, Medium, Hard rather than All, Easy, Hard, Medium.

The comparator reuses the LEVELS array from web/problem-picker.js, which web/progress.js already imports to decide which difficulties to allow, so the scale stays defined once. A new test covers all three levels because Easy and Medium sort the same either way, so the existing test could not catch the bug.

Closes #281.

^{Written for commit 1f5a993. Summary will update on new commits.}

[ColtenOuO]

Overall, the behavior looks good to me, but I have a few thoughts on the newly added comment.

[ColtenOuO]

Thanks, LGTM.

[jserv]

Thank @Pandamachi for contributing!