feat(pen-codegen): skeleton crate (bucket A)

crates/pen-codegen/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "pen-codegen"
+version.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+description = "OpenPencil codegen (.op → React/Vue/Svelte/...) — bucket A in-WASM"
+
+[lib]
+name = "pen_codegen"
+path = "src/lib.rs"
+
+[dependencies]
+pen-types = { path = "../pen-types" }

crates/pen-codegen/src/lib.rs

@@ -0,0 +1,5 @@
+//! OpenPencil codegen.
+
+pub fn placeholder() -> String {
+    format!("pen-codegen ({})", pen_types::placeholder())
+}