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/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "ostp-gui"
+version.workspace = true
+edition.workspace = true
+description = "OSTP Windows GUI Client"
+
+[build-dependencies]
+tauri-build = { version = "2", features = [] }
+
+[dependencies]
+tauri = { version = "2", features = ["protocol-asset"] }
+tauri-plugin-shell = "2"
+serde.workspace = true
+serde_json.workspace = true
+tokio.workspace = true
+anyhow.workspace = true
+
+[target.'cfg(windows)'.dependencies]
+winapi = { version = "0.3", features = ["winbase", "namedpipeapi", "fileapi"] }