feat: add comprehensive integration test suite (#3)

* feat: add comprehensive integration test suite

29 integration tests covering all CLI subcommands (check, coverage,
generate, init), global flags (--strict, --require-coverage, --root),
multi-language support (TypeScript, Rust, Go, Python), and error cases
(missing files, invalid frontmatter, phantom exports, missing sections).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: resolve CI failures — cargo fmt + Windows-compatible temp dir

- Run cargo fmt to fix formatting issues across multiple files
- Replace hardcoded "/tmp" with std::env::temp_dir() in
  root_flag_overrides_cwd test for Windows compatibility

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: corvid-agent