feat: bundle XeXTool with xorloser attribution

[TrapEmAll]

Summary

• bundles XeXTool 6.3 in the Windows application resources
• automatically selects the bundled executable when no valid custom path is configured
• keeps support for user-selected XeXTool builds and other command-line utilities
• credits xorloser in both External Tools and Help & About
• preserves the source project's GPL-3.0 license alongside the binary
• adds a third-party notice with source provenance and the exact SHA-256 checksum
• includes the binary, license, and notice in PyInstaller releases
• leaves Linux behavior unchanged: users can select native tools or their own trusted wrapper

Provenance and attribution

The bundled xextool.exe is sourced from XboxChef/XexToolGUI, which identifies it as XeXTool 6.3 by xorloser and distributes the repository under GPL-3.0. The copied binary has SHA-256 D93C1B814AD6FF124834F4235BF8AAC9F09DBA8D69C335EBECC8D6EFE8D5A062.

No Xbox SDK files, keys, firmware, or game content are included.

Validation

• 81 tests passed
• Ruff passed
• focused mypy checks passed
• Windows PyInstaller build completed successfully
• inspected the packaged executable and confirmed it contains XeXTool, the preserved GPL text, and THIRD_PARTY_NOTICES.md
• XboxUnity remains HTTP-only