fix: show live run names before completion

[christso]

Summary

• infer experiment names for live run metadata before result rows persist them
• use shared Studio run-label formatting in the run list and sidebar
• cover both single-benchmark and multi-benchmark live-run paths with regressions

Closes #1198

Red/green verification

Red

While a run was still active, /api/runs returned the live run with a timestamp display name and no experiment:

{
  "filename": "issue-1198-live-name::2026-04-29T09-17-30-111Z",
  "display_name": "2026-04-29T09-17-30-111Z",
  "target": "llm-dry-run"
}

That made Studio show the timestamp instead of the final target/experiment-derived label.

Green

Replaying the same scenario after the fix returned the live run with the experiment available immediately:

{
  "filename": "issue-1198-live-name-fixed::2026-04-29T09-24-12-067Z",
  "display_name": "2026-04-29T09-24-12-067Z",
  "target": "llm-dry-run",
  "experiment": "issue-1198-live-name-fixed",
  "label": "llm-dry-run · issue-1198-live-name-fixed"
}

So the in-progress run now uses the same final label inputs before completion.

Validation

• bun test apps/cli/test/commands/results/serve.test.ts apps/studio/src/components/run-eval-threshold.test.ts apps/studio/src/lib/run-label.test.ts
• bun run lint