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

Cargo.toml

@@ -0,0 +1,7 @@
+[workspace]
+resolver = "2"
+members = [
+    "common",
+    "server",
+    "stub"
+]