feat(spotlight): readable cards with TL;DR + inline values

[coccyx]

Summary

Stacked on PR #53. After the scoped-baseline fix landed, manual feedback was:

I see one thing — rpc.grpc.status_code — and I still don't understand how to read this or how it helps me find things.

The chart-only design hid the actual information (value names, counts, percentages) behind a click. Visual asymmetry told users "something differs" without telling them what, or what to do about it.

Each attribute card now leads with words and numbers; the chart is a scanning aid, not the primary readout.

What changed in each card

1. TL;DR headline sentence above the chart. Picks the strongest single value (largest |diff|) and writes it out: "Selection over-represents 13 by +100.0 pp (144 sel vs 0 base)."
2. Inline value rows below the chart — top 3 by default — with per-row counts, percentages, and a dedicated "Search →" button. No click required to see the substance.
3. Plain-English legend at the panel bottom: "selection (the spans you're investigating)" / "baseline (what they're being compared against)". The earlier "sel"/"base" jargon assumed background the novice user doesn't have.
4. "Show N more values" toggle for the long tail.

Same engine, same scoped-baseline data — purely a readability change. SpotlightSection (Errors, Service Detail) inherits.

What payment now reads as

	value	diff	counts
▏	0	-100.0 pp	sel 0 (0%), base 905 (100%)
▎	13	+100.0 pp	sel 144 (100%), base 0 (0%)

Plain reading: failing payment.Charge calls all return gRPC status 13; healthy ones all return 0. Click Search next to 13 to see the matching error spans.

Test plan

• npx tsc --noEmit — clean
• npm run lint — 0 errors
• npm test — 104/104 passing
• npm run deploy — packed + uploaded + provisioned on staging
• Playwright capture spec succeeds

Validate on staging

paymentFailure 50% is still on.

1. Open Services → payment. Spotlight section now has:
   • Header: rpc.grpc.status_code + score chip
   • Headline sentence underneath
   • Mini chart
   • Two value rows with counts, percentages, and Search buttons — visible without any clicks
2. Click Search → next to 13 — opens Traces with the matching filter applied.

Stacking

Based off PR #53 (scoped baseline). Merge that first; this PR will become a clean diff against master after.

🤖 Generated with Claude Code