analytics: make table sorting consistent (default direction, keyboard access, locale compare, one shared helper) #236

Relates to #226, #230

Problem

The #230 review found that the analytics page now has three local table sorts that behave differently:

• sortChannels (the channel table);
• makeAreasSection (Areas);
• sortMbAdopterRows (Hash Stats, fix(analytics): sort the Hash Stats adopters table by the clicked column, with direction (#226) #230).

1. Default direction (UX).
   • Hash Stats starts every column ascending, so a first click on Adverts shows the fewest first, and a first click on Last Seen shows the oldest first.
   • The channel table (analytics.js ~1462: name/hash asc, otherwise desc) and Areas (ascByDefault, desc by default) start numeric and time columns descending.
2. Keyboard access and a11y.
   • The sortable <th> headers in the channel table and in Hash Stats have no tabindex and no <button>, so they cannot be reached by keyboard.
   • The ⇅/↑/↓ span from channelSortArrow has no aria-hidden="true", so the glyph becomes part of each header's accessible name. aria-sort is set in Hash Stats, which makes the glyph redundant there.
3. Locale-aware compare. Node and Role names are compared as lower-cased strings by code point. Names starting with Æ/Ø/Å, accented letters or emoji therefore sort after z. localeCompare (or Intl.Collator) would place them naturally.
4. DRY. The fix(analytics): sort the Hash Stats adopters table by the clicked column, with direction (#226) #230 comparator is stable through an index tie-break and puts NaN last in both directions, which makes it the most complete of the three. It is a good candidate for a shared helper.

Proposed fix

• Extract one shared sort helper (comparator plus header state) and use it for the channel table, Areas and Hash Stats.
• Give each column a default direction: text ascending, numbers and times descending.
• Render sortable headers as <button>s inside <th>, or make them focusable with Enter/Space handling. Keep aria-sort, and mark the arrow glyph aria-hidden="true".
• Use localeCompare / Intl.Collator for text columns.
• Keep the existing deep links (mbsort=/mbdir= and any channel-table params) working unchanged.

Acceptance

• The same column types start in the same direction in all three tables, and unit tests pin the first-click direction per column type.
• Every sortable header can be reached with Tab and sorted with Enter/Space, with no glyph in the accessible name. Covered by an E2E.
• Names starting with Æ/Ø/Å sort in locale order, with a unit test.
• There is one comparator implementation. No hardcoded colours, and scripts/check-xss-sinks.sh --diff is clean.