feat: Add native Linux/macOS installation support

- Create Install-Claude.sh for native Bash installation
- Update install-remote.sh to call Install-Claude.sh instead of PowerShell
- Move installation section to top of README files
- Add prominent shell installation instructions for all platforms
- Support true cross-platform installation without PowerShell dependency

Installation methods:
- Windows: PowerShell (install-remote.ps1 + Install-Claude.ps1)
- Linux/macOS: Bash (install-remote.sh + Install-Claude.sh)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: catlog22