fix(tools): harden scheduler limits and logs

Guard scheduler system actions against pending work, serialize diagnostic log transitions, and keep speed-limit saves truthful after backend failures.\n\nNo linked issue was found for this audit.

src/components/SpeedLimiterView.test.ts

@@ -0,0 +1,11 @@
+import { describe, expect, it } from 'vitest';
+import { displayValueFromPresetBase, presetBaseFromDisplayValue } from './SpeedLimiterView';
+
+describe('SpeedLimiterView speed conversions', () => {
+  it('converts KB/s and MB/s using binary units consistently', () => {
+    expect(presetBaseFromDisplayValue(1024, 'KB/s')).toBe(1);
+    expect(displayValueFromPresetBase(1, 'KB/s')).toBe(1024);
+    expect(presetBaseFromDisplayValue(5, 'MB/s')).toBe(5);
+    expect(displayValueFromPresetBase(5, 'MB/s')).toBe(5);
+  });
+});