Add examples catalog with subcommand dispatch

- Extract game engine from package main to engine/ library package
- Create examples/ package with registry, Entry type, and BuilderDeps
- Register default world as an example (moved from main())
- Add combat example: two teams of units facing each other
- Rewrite main.go as thin dispatch: go run . example [name]
- Update README with examples catalog one-liner

1 files changed, 2 insertions, 0 deletions

diff --git a/README.md b/README.md
index 6f07ced..4a4ee87 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,5 @@
+Run `go run . example` to browse and launch curated gameplay scenarios (combat, gathering, etc.)  
+
 ## Debugging
 
 - Restart after kernel update until `glxinfo | grep "OpenGL version"` works