Track generated files in repository

Remove *_gen.go from .gitignore to track generated code examples.
This allows users to see the output of the code generator without
needing to run the build process.

Includes:
- Calculator example generated files (app_gen.go, calculator_gen.go, guix_helpers_gen.go)
- Counter example generated files

All generated files include:
- Proper build tags (//go:build js && wasm)
- Correct parameter reference handling
- Proper initialization vs render separation

Author: claude

.gitignore

@@ -16,9 +16,6 @@ go.work
 wasm_exec.js
 main.wasm
 
-# Generated files
-*_gen.go
-
 # Cache
 .guix/
 *.cache