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>

viewer/build.rs

@@ -0,0 +1,9 @@
+use std::io::Result;
+
+fn main() -> Result<()> {
+    println!("cargo:rerun-if-changed=../proto/guruconnect.proto");
+
+    prost_build::compile_protos(&["../proto/guruconnect.proto"], &["../proto/"])?;
+
+    Ok(())
+}