feat(ui): multi-select group-by for Recent Runs by Client

[skylenet]

The suite-details "Group by" (Recent Runs by Client) previously allowed only a single value. It's now multi-select and defaults to all available labels, so runs group by the combination — e.g. selecting aot + bal-mode groups by aot=…, bal-mode=….

Changes

• SuiteDetailPage.tsx
  • groupBy URL param semantics: unset = all label keys (the new default), none = no grouping, otherwise a comma-separated key list (aot,bal-mode). New parseGroupByKeys/serializeGroupByKeys helpers mirror the existing steps param convention.
  • effectiveGroupBy (single) → effectiveGroupByKeys: string[]. applyGrouping builds a composite key=value, key=value suffix on the client name.
  • The selector becomes a multi-toggle row (like "Metric steps"): None clears grouping; each label and instance id toggle independently.
  • All four compare-URL builders emit correct multi-key group specs.
• RunsHeatmap.tsx: groupBy?: string → string[]. It composites each run's group value, carries a per-group metadata map, renders the key=value composite in the group header, and passes the metadata map to getGroupCompareGroupHref so it can emit client:k1=v1,k2=v2.

The /compare/groups group-spec parser already ANDs multiple key=value conditions per group, so no compare-page changes were needed.

Notes

• Grouping by instance_id combines with labels; it's excluded from the compare metadata filter (it isn't a metadata key) exactly as before.
• Display format is key=value pairs (disambiguates which value belongs to which label).

Validation

No UI test suite exists; verified with tsc -b, eslint, and a full vite build — all clean.