fix(ui): compare-groups crash with 6+ groups + responsive filter UX

[skylenet]

Summary

• Crash fix: RUN_SLOTS extended from 5 to 10 entries (A–J) so URLs comparing more than 5 groups (e.g. all six EL clients) no longer crash on RUN_SLOTS[r.index].label being undefined. GroupBuilder cap raised from 5 to RUN_SLOTS.length.
• Per-group loading spinners on the compare-groups builder: each card now shows a small "Loading…" spinner in its header while that group's config or any of its sampled result fetches are in-flight, instead of relying solely on the global state.
• Non-blocking filter updates on both compare pages: filter URL writes (search box, regex toggle, chip toggles, gas-bucket buttons, diff filter) now run inside useTransition. Chip clicks and keystrokes paint immediately while the fan-out re-renders (charts × runs × thousands of tests) happen as an interruptible transition — rapid clicks cancel in-flight work instead of queueing 4s hangs per click.
• Quieter dimension breakdown: when only 1–2 dimensions are available, the "Show more / Show fewer dimensions" toggle is hidden entirely (nothing to collapse). Reappears automatically with 3+ dimensions. Applied in both DimensionInsights and CompareDimensionInsights.

Test plan

• Open /compare/groups?suite=…&groups=besu:;;erigon:;;ethrex:;;geth:;;nethermind:;;reth: — confirm the page renders without throwing on slot.label and each group gets a distinct color (A–F).
• In the group builder, while results are still loading, confirm each group card shows a small spinner in its header alongside the "X runs found" badge.
• On /compare?runs=… and /compare/groups?… with thousands of tests, click a facet chip rapidly several times — the click should feel instant; older work should be cancelled rather than queued.
• In the dimension breakdown panel: with a filter narrow enough that only 1–2 dimensions remain, confirm both are visible and no toggle button is shown. Loosen the filter so 3+ dimensions appear and confirm the toggle reappears.