Add an interactive OS selector widget to the hero section and install
steps, inspired by OpenClaw's install UI:
- macOS-style window chrome with red/yellow/green dots
- Three clickable tabs: Linux/macOS, PowerShell, CMD
- Command text, shell prompt, and note update on tab click
- Auto-detects visitor's OS and selects the right tab on page load
- Install steps section also gets synced platform tabs
- Simplified Windows note section (tabs above now cover all platforms)
- Fully responsive — icons hidden on mobile, tabs wrap properly
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