init: FileDrop phase1 architecture and scaffold

- Rust axum signaling server with WebSocket support
- Lit + TypeScript frontend with Vite
- Redis session storage with TTL
- WebRTC transport and crypto client stubs
- Phase1 architecture plan in plans/
- Deploy directory structure prepared

server/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "filedrop-server"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+axum = { version = "0.7", features = ["ws"] }
+tokio = { version = "1", features = ["full"] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+redis = { version = "0.25", features = ["tokio-comp", "connection-manager"] }
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+rand = "0.8"
+thiserror = "1"
+config = "0.14"
+chrono = "0.4"
+base64-url = "2"
+futures = "0.3"