fix: normalize guild stock targets invariantly

[vycdev2]

Summary

• normalize stock target keywords with invariant casing so GUILD works under cultures such as tr-TR
• add a culture-specific regression test and document the fix

Verification

• LD_LIBRARY_PATH=/tmp/hermes-icu76/root/usr/lib/x86_64-linux-gnu DOTNET_SYSTEM_GLOBALIZATION_INVARIANT=0 dotnet test — passed: 557 tests, 0 skipped
• dotnet build — passed with 0 warnings and 0 errors
• python3 -m unittest tools.test_generate_commands_md — passed: 3 tests
• git diff --check — passed

Risk

• Low: the change only makes casing deterministic for existing stock target keywords.

This was generated by an AI agent (vycdev2). Please verify any changes before merging or applying.