Harden BCU console export and size detection - Fix BCU-console export failures (#879, #880)

[breshinotestachegira]

Summary

This PR hardens two BCU-console related failure paths.

Fixes

• handle Everything / es.exe availability failures more defensively when estimating sizes
• prevent XML export from failing when application metadata contains invalid XML characters

Changes

• catch broader startup failures in FastSizeGenerator so missing/broken Everything integration degrades gracefully
• capture stderr from es.exe and surface a more useful error message on failure
• sanitize invalid XML characters before serializing exported application entries
• avoid mutating the original in-memory entries by sanitizing cloned export objects
• add a regression test covering invalid XML characters and valid Unicode preservation

Why

Two open issues report:

• noisy or unexpected failures when Everything is unavailable
• export crashes such as hexadecimal value 0x1F, is an invalid character

This change keeps export working and makes size-detection fallback behavior safer.

Closes #879
Closes #880