Add native viewer with low-level keyboard hooks

- New viewer crate for Windows native remote desktop viewing
- Implements WH_KEYBOARD_LL hook for Win key, Alt+Tab capture
- WebSocket client for server communication
- softbuffer rendering for frame display
- Zstd decompression for compressed frames
- Mouse and keyboard input forwarding

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Cargo.toml

@@ -3,6 +3,7 @@ resolver = "2"
 members = [
     "agent",
     "server",
+    "viewer",
 ]
 
 [workspace.package]