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>
