feat: cross-platform support (Linux and macOS)

[relmer]

Summary

Port TCDir to Linux and macOS, enabling the same colorized directory listing experience across platforms.

Details

Platform Abstractions Needed

• Console output: Replace Windows Console API (WriteConsoleW) with ANSI escape sequences (already used for color — extend to full output path)
• File attributes: Map NTFS attributes (RHSDA) to POSIX equivalents (permissions, hidden-by-convention)
• File enumeration: Replace FindFirstFileW/FindNextFileW with opendir/readdir or platform-native equivalents
• Cloud status: OneDrive/iCloud detection is Windows-specific — gracefully disable or add platform-specific providers
• NTFS streams: Windows-only — disable on other platforms
• File owner: Replace Windows SID lookup with stat() uid/gid resolution
• Nerd Font detection: Replace GDI-based detection with terminal capability probing
• Icon mappings: Largely portable (file extension based)
• Wide string handling: Replace wchar_t/LPCWSTR with UTF-8 throughout

Architecture Considerations

• TCDir is C++/Win32 — this would be a significant refactor
• RCDir (Rust) may be a more natural vehicle for cross-platform, but that decision is deferred
• Could use #ifdef platform gating or a platform abstraction layer
• Consider whether to maintain a single codebase or fork for platform-specific builds

Build System

• CMake or Meson for cross-platform builds (replacing MSBuild/vcxproj)
• CI: add Linux and macOS runners to GitHub Actions

Priority

• This is a large undertaking — likely a multi-release effort
• Start with Linux (most demand), then macOS

Prior Art

• eza: Rust, cross-platform from the start
• lsd: Rust, cross-platform
• Both demonstrate that the feature set translates well across platforms

Notes

• The vehicle for cross-platform (TCDir C++ vs RCDir Rust) is an open question
• RCDir's Rust codebase with cfg(target_os) gating would be significantly less work
• This issue is for tracking the idea — actual implementation approach TBD