Add create-plugin command and improve asset management

- Add new create-plugin command to generate plugins from starter template
- Add manifest name subcommand for template context
- Replace hardcoded asset paths with explicit file patterns in embed directive
- Refactor asset build system to use _setup.mk instead of setup.mk
- Update versioning to use pluginctl manifest id for APP_NAME
- Clean up Makefile by removing redundant bundle name definition

🤖 Generated with [Claude Code](https://claude.ai/code)

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

updateassets.go

@@ -13,7 +13,7 @@ import (
 	"github.com/mattermost/mattermost/server/public/model"
 )
 
-//go:embed assets/*
+//go:embed assets/.editorconfig assets/.gitattributes assets/.nvmrc assets/Makefile assets/*.yml assets/build/*.mk assets/.github/**/*.yml assets/webapp/.npmrc assets/webapp/*.config.js
 var assetsFS embed.FS
 
 const (