EZC: Add C/C++ to CodeQL security scanning

## Add C to CodeQL

C code is now in the repo (`ezc/`). CodeQL needs to scan it for security vulnerabilities — buffer overflows, format string bugs, use-after-free, etc.

### Checklist
- [ ] Add `cpp` to CodeQL language matrix (or create new CodeQL workflow if none exists)
- [ ] Verify CodeQL runs on PRs touching `ezc/` files
- [ ] Review and address any initial findings