chore: rename app crate and binary to cyberpunk

The game is called cyberpunk; the city generator is its first subsystem,
not the project. The citygen library keeps its name. README reframed
around the game.

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

Cargo.lock

@@ -121,22 +121,6 @@ version = "1.0.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4e7648175b45a9a48536d676f68d918270699102aa8dab5496df06904c914600"
 
-[[package]]
-name = "city"
-version = "0.1.0"
-dependencies = [
- "anyhow",
- "citygen",
- "clap",
- "crossterm",
- "postcard",
- "ratatui",
- "ron",
- "serde",
- "serde_json",
- "unicode-width 0.2.0",
-]
-
 [[package]]
 name = "citygen"
 version = "0.1.0"
@@ -250,6 +234,22 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "cyberpunk"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "citygen",
+ "clap",
+ "crossterm",
+ "postcard",
+ "ratatui",
+ "ron",
+ "serde",
+ "serde_json",
+ "unicode-width 0.2.0",
+]
+
 [[package]]
 name = "darling"
 version = "0.24.1"