fix(filesystem): handle negative values in formatSize() (#3231)

Return '0 B' for negative byte values instead of 'NaN B'.
File sizes cannot be negative, so this is a safe default.

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

src/filesystem/__tests__/lib.test.ts

@@ -65,8 +65,10 @@ describe('Lib Functions', () => {
       });
 
       it('handles negative numbers', () => {
-        // Negative numbers will result in NaN for the log calculation
-        expect(formatSize(-1024)).toContain('NaN');
+        // Negative numbers should return '0 B' as file sizes cannot be negative
+        expect(formatSize(-1)).toBe('0 B');
+        expect(formatSize(-1024)).toBe('0 B');
+        expect(formatSize(-1000000)).toBe('0 B');
         expect(formatSize(-0)).toBe('0 B');
       });