Split core library and CLI workspace

crates/decodal-cli/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "decodal"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+decodal-core = { path = "../decodal-core" }

crates/decodal-cli/src/main.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("Decodal {}", decodal_core::version());
+}