deploy-agent: Rust deployment automation (server + stub + signed payloads)

- Workspace: common (protocol/crypto/tarball), server (axum+rustls), stub (registration, poll, verify-before-execute)
- Ed25519 payload signing + request-signature auth on /poll, /report
- flate2/miniz_oxide pure-Rust tarball, no system deps
- CI matrix: linux musl x86_64/aarch64, windows x86_64
- Compiles clean: cargo build --workspace, 0 errors 0 warnings

common/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "common"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
+ed25519-dalek = "2.1"
+rand = "0.8"
+flate2 = { version = "1.0", default-features = false, features = ["rust_backend"] }
+tar = "0.4"
+hex = "0.4"
+sha2 = "0.10"
+thiserror = "1.0"