CLAUDE.md and CODEX.md already documented that CA1416 is suppressed solution-wide via the root .editorconfig; copilot-instructions.md was missing that note, breaking the three-file sync rule the header of each file requires. Also adds the .editorconfig itself, which the note references and which was untracked. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>