refactor: workspace scaffolding — sunbeam-sdk + sunbeam binary crate

Convert the single binary crate into a Cargo workspace with two members:
sunbeam-sdk (library) and sunbeam (thin binary). Moves build.rs to the
SDK with adjusted .git/HEAD path for the nested layout.

Cargo.toml

@@ -1,63 +1,3 @@
-[package]
-name = "sunbeam"
-version = "0.1.0"
-edition = "2024"
-description = "Sunbeam local dev stack manager"
-
-[dependencies]
-# Core
-thiserror = "2"
-tokio = { version = "1", features = ["full"] }
-clap = { version = "4", features = ["derive"] }
-serde = { version = "1", features = ["derive"] }
-serde_json = "1"
-serde_yaml = "0.9"
-tracing = "0.1"
-tracing-subscriber = { version = "0.3", features = ["env-filter"] }
-
-# Kubernetes
-kube = { version = "0.99", features = ["client", "runtime", "derive", "ws"] }
-k8s-openapi = { version = "0.24", features = ["v1_32"] }
-
-# HTTP + TLS
-reqwest = { version = "0.12", features = ["json", "rustls-tls", "blocking"] }
-rustls = { version = "0.23", features = ["ring"] }
-
-# SSH
-russh = "0.46"
-russh-keys = "0.46"
-
-# Crypto
-rsa = "0.9"
-pkcs8 = { version = "0.10", features = ["pem"] }
-pkcs1 = { version = "0.7", features = ["pem"] }
-sha2 = "0.10"
-hmac = "0.12"
-base64 = "0.22"
-rand = "0.8"
-
-# Certificate generation
-rcgen = "0.14"
-
-# SMTP
-lettre = { version = "0.11", default-features = false, features = ["smtp-transport", "tokio1-rustls-tls", "builder", "hostname"] }
-
-# Archive handling
-flate2 = "1"
-tar = "0.4"
-
-# Async
-futures = "0.3"
-tokio-stream = "0.1"
-
-# Utility
-tempfile = "3"
-dirs = "5"
-chrono = { version = "0.4", features = ["serde"] }
-
-[build-dependencies]
-reqwest = { version = "0.12", features = ["blocking", "rustls-tls"] }
-sha2 = "0.10"
-flate2 = "1"
-tar = "0.4"
-chrono = "0.4"
+[workspace]
+members = ["sunbeam-sdk", "sunbeam"]
+resolver = "3"