Harden RC9 UX and performance states

frontend/src/lib/performanceBudget.test.ts

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+import { describe, expect, it } from 'vitest'
+import {
+  COVERAGE_RESPONSE_BUDGET_MS,
+  MAP_ANALYSIS_BUDGET_MS,
+  exceedsPerformanceBudget,
+  formatPerformanceDuration,
+} from './performanceBudget'
+
+describe('release performance budgets', () => {
+  it('keeps coverage stricter than complete map analysis', () => {
+    expect(COVERAGE_RESPONSE_BUDGET_MS).toBe(4_000)
+    expect(MAP_ANALYSIS_BUDGET_MS).toBe(15_000)
+  })
+
+  it('only marks completed work above its budget as slow', () => {
+    expect(exceedsPerformanceBudget(null, 4_000)).toBe(false)
+    expect(exceedsPerformanceBudget(4_000, 4_000)).toBe(false)
+    expect(exceedsPerformanceBudget(4_001, 4_000)).toBe(true)
+  })
+
+  it('formats timings for compact operator feedback', () => {
+    expect(formatPerformanceDuration(null)).toBeNull()
+    expect(formatPerformanceDuration(238)).toBe('238 ms')
+    expect(formatPerformanceDuration(1_250)).toBe('1,3 s')
+  })
+})

frontend/src/lib/performanceBudget.ts

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+export const COVERAGE_RESPONSE_BUDGET_MS = 4_000
+export const MAP_ANALYSIS_BUDGET_MS = 15_000
+
+export function exceedsPerformanceBudget(
+  durationMs: number | null,
+  budgetMs: number,
+): boolean {
+  return durationMs !== null && durationMs > budgetMs
+}
+
+export function formatPerformanceDuration(durationMs: number | null): string | null {
+  if (durationMs === null) return null
+  if (durationMs < 1_000) return `${Math.max(1, Math.round(durationMs))} ms`
+  return `${(durationMs / 1_000).toLocaleString('nl-BE', {
+    maximumFractionDigits: 1,
+    minimumFractionDigits: 1,
+  })} s`
+}