feat: Windows stack (daemon, installer, GUI)

Components:
- ostp-daemon: Windows Service with Named Pipe IPC
- ostp-installer: Setup wizard with admin privileges
- ostp-gui: Tauri dark theme UI (450x600)

Features:
- Background service management (OspabGuard)
- IPC commands: CONNECT/DISCONNECT/STATUS
- Firewall rules auto-configuration
- Wintun driver placeholder (download from wintun.net)
- Real-time stats display (upload/download/ping)

Note: Requires wintun.dll download for full functionality

ostp-gui/src/ipc.rs

@@ -0,0 +1,39 @@
+//! IPC communication with ostp-daemon via Named Pipe
+
+use anyhow::{Context, Result};
+use std::io::{Read, Write};
+
+const PIPE_NAME: &str = r"\\.\pipe\ostp-daemon";
+
+pub async fn send_command(command: &str) -> Result<String> {
+    #[cfg(windows)]
+    {
+        use std::fs::OpenOptions;
+        use std::os::windows::fs::OpenOptionsExt;
+        use winapi::um::winbase::FILE_FLAG_OVERLAPPED;
+
+        // Connect to Named Pipe
+        let mut pipe = OpenOptions::new()
+            .read(true)
+            .write(true)
+            .custom_flags(FILE_FLAG_OVERLAPPED)
+            .open(PIPE_NAME)
+            .context("Failed to connect to ostp-daemon. Is the service running?")?;
+
+        // Send command
+        pipe.write_all(command.as_bytes())?;
+        pipe.write_all(b"\n")?;
+        pipe.flush()?;
+
+        // Read response
+        let mut response = String::new();
+        pipe.read_to_string(&mut response)?;
+
+        Ok(response.trim().to_string())
+    }
+
+    #[cfg(not(windows))]
+    {
+        anyhow::bail!("Named pipes are only supported on Windows");
+    }
+}