fix(settings): preserve speed limiter units

Persist the selected display unit for disabled limits, preserve in-progress fractional input, and keep exact KiB-backed preset values visible.\n\nNo linked issue.

src/components/SpeedLimiterView.test.ts

@@ -1,7 +1,11 @@
 import { describe, expect, it } from 'vitest';
 import {
   convertSpeedValue,
+  clampSpeedDisplayValue,
   displayValueFromPresetBase,
+  formatSpeedLimitForStorage,
+  formatPresetValue,
+  parseLimit,
   presetBaseFromDisplayValue,
 } from './SpeedLimiterView';
 
@@ -20,4 +24,33 @@ describe('SpeedLimiterView speed conversions', () => {
     expect(convertSpeedValue(1500, 'KB/s', 'MB/s')).toBe(1500 / 1024);
     expect(convertSpeedValue(convertSpeedValue(1500, 'KB/s', 'MB/s'), 'MB/s', 'KB/s')).toBe(1500);
   });
+
+  it('preserves the selected unit when saving a non-MiB-aligned MB/s value', () => {
+    const storedLimit = formatSpeedLimitForStorage(1.5, 'MB/s');
+
+    expect(storedLimit).toBe('1.5M');
+    expect(parseLimit(storedLimit, 1024)).toEqual({ value: 1.5, unit: 'MB/s' });
+  });
+
+  it('preserves an explicitly selected KB/s unit at MiB boundaries', () => {
+    const storedLimit = formatSpeedLimitForStorage(1024, 'KB/s');
+
+    expect(storedLimit).toBe('1024K');
+    expect(parseLimit(storedLimit, 1)).toEqual({ value: 1024, unit: 'KB/s' });
+  });
+
+  it('restores the persisted unit while the limiter is disabled', () => {
+    expect(parseLimit('', 1536, 'MB/s')).toEqual({ value: 1.5, unit: 'MB/s' });
+    expect(parseLimit('', 1536, 'KB/s')).toEqual({ value: 1536, unit: 'KB/s' });
+  });
+
+  it('allows sub-one MB/s values while enforcing the 1 KiB backend minimum', () => {
+    expect(clampSpeedDisplayValue(0.5, 'MB/s')).toBe(0.5);
+    expect(clampSpeedDisplayValue(0, 'MB/s')).toBe(1 / 1024);
+    expect(clampSpeedDisplayValue(0, 'KB/s')).toBe(1);
+  });
+
+  it('shows the exact stored preset value instead of a rounded label', () => {
+    expect(formatPresetValue(1.46484375)).toBe('1.46484375');
+  });
 });