Add .gitattributes rules so .c/.h/.cpp/.hpp are always stored as LF
(prevents EOL drift from editors with autocrlf-true defaults), and
renormalize the 30 source files that had drifted to CRLF in the index.
Pure mechanical change — `git diff --ignore-cr-at-eol` is empty.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>