Feature: "show all groups" control for dimensions with more than 12 groups in the web profiler #740

Where: assets/profiler-ui.js (dimCard), assets/profiler-compare.js, faircode/SPEC.md section 7.

Current gap: DISPLAY_GROUPS = 12 (explicitly commented "mirror faircode/report.py") truncates every dimension's bar-chart display to the first 12 groups; when a dimension (e.g. a high-cardinality geography column) has more, the UI only renders a static line: '<div class="dim-more">… and ' + (d.groups.length - DISPLAY_GROUPS) + ' more groups</div>' with no button, link, or expand affordance - grep -n "showMore\|expand" assets/profiler-ui.js returns nothing. The only way to see the remaining groups is to leave the visual UI and use "Copy as JSON" to inspect raw text, or switch to the CLI's --json. SPEC.md section 7 mandates the truncation and the omitted-count message but doesn't require (or forbid) a way to actually view the rest.

Repro:

$ grep -n "DISPLAY_GROUPS\|dim-more" assets/profiler-ui.js
11: DISPLAY_GROUPS = 12  // mirror faircode/report.py
...: '<div class="dim-more">… and ' + (d.groups.length - DISPLAY_GROUPS) + ' more groups</div>'
$ grep -n "showMore\|expand" assets/profiler-ui.js
(no output)

Suggested approach: make the "… and N more groups" text an actual <button> that expands the same dim-card in place to show the full d.groups list (same bar-row markup, just without the slice(0, DISPLAY_GROUPS) cap), toggling back to "Show fewer" - same pattern for the dim-reference and compare's cd.groups truncation.