fix(monitoring): label KPI charts for screen readers

[pedrofrxncx]

The KPI charts in the org monitoring dashboard (Tool Calls, Latency, Errors, and the AI Usage row) render as bare recharts SVGs with no accessible name — a screen reader user landing on one gets either silence or a jumble of raw SVG element announcements, with no indication of what metric the chart shows.

Adds a required ariaLabel prop to KPIChart and forwards it to the underlying ChartContainer div as role="img" + aria-label, then supplies a concrete label at each of the 8 call sites in the monitoring overview tab (e.g. "Tool calls over time", "Average latency over time", "AI errors over time").

This directly improves accessibility of the monitoring widgets, the stated focus for this area, with no behavior change to the rendered chart itself — only an added ARIA label.

To verify: open a browser's accessibility tree / VoiceOver on the org monitoring page and confirm each chart card now announces a descriptive label instead of nothing.

Locally ran: bun run fmt (clean) and cd apps/mesh && bunx tsc --noEmit (clean, confirms the now-required ariaLabel prop is supplied everywhere KPIChart is used). Full CI validates lint and the rest of the suite.

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Summary by cubic

Adds accessible names to monitoring KPI charts so screen readers announce what each chart shows. No visual changes.

• Bug Fixes
  • Made ariaLabel required on KPIChart and forwarded as role="img" + aria-label on the container.
  • Labeled all 8 charts in the org monitoring overview (Tool calls, Latency avg/P95, Errors, AI usage: calls, tokens, cost, latency, errors).

^{Written for commit b2862b7. Summary will update on new commits.}