feat(city): animated generating screen

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

crates/city/src/walker/mod.rs

@@ -0,0 +1,5 @@
+//! The walker: the player's `@`, movement, connectors and field of view.
+
+/// The player. Filled in by the walker task; declared here so app state can hold one.
+#[derive(Clone, Debug)]
+pub struct Player;