chore: cargo workspace with citygen and city crates

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

crates/citygen/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "citygen"
+edition.workspace = true
+version.workspace = true
+license.workspace = true
+
+[dependencies]
+serde.workspace = true
+rand.workspace = true
+rand_chacha.workspace = true
+noise.workspace = true
+thiserror.workspace = true
+ron.workspace = true

crates/citygen/src/lib.rs

@@ -0,0 +1 @@
+//! World model and generator for the cyberpunk city.