feat(rust): add shared Signal client and workspace configuration

rust/signal/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "signal"
+version = "0.1.0"
+edition = "2024"
+description = "Send Signal alerts through the local signal-cli JSON-RPC daemon"
+license = "MIT"
+publish = false
+
+[dependencies]
+anyhow.workspace = true
+serde_json.workspace = true
+
+[target.'cfg(target_os = "linux")'.dev-dependencies]
+libc = "0.2"
+
+[lints]
+workspace = true