fix(trajectory): show exact millisecond durations consistently

Drop the details-panel Duration toggle: Duration rows always show
integer milliseconds, matching the cell time column. Timeline labels
(Total/TTFT/Decoding) and step-group descriptions previously fell back
to second labels at or above one second; they now also show exact
milliseconds via the shared formatDurationMillis formatter.

packages/client/ui-trajectory/tests/views.spec.tsx

@@ -580,9 +580,9 @@ describe('timeline projection', () => {
       expect(view.container.querySelector('[role="tooltip"]')).toBeNull()
       act(() => { vi.advanceTimersByTime(1) })
       const tooltip = view.container.querySelector<HTMLElement>('[role="tooltip"]')
-      expect(tooltip?.textContent).toContain('Total 2.0 s')
+      expect(tooltip?.textContent).toContain('Total 2,000 ms')
       expect(tooltip?.textContent).toContain('TTFT 500 ms')
-      expect(tooltip?.textContent).toContain('Decoding 1.5 s')
+      expect(tooltip?.textContent).toContain('Decoding 1,500 ms')
     } finally {
       vi.useRealTimers()
     }