add build, DMG creation scripts, CI/CD workflows

- build-bundle.sh: regenerates Info.plist with KLInfo entries for all 4
  layout versions, sets CalVer bundle version, validates plists
- create-dmg.sh: packages bundle into a DMG with drag-and-drop symlink
  to /Library/Keyboard Layouts/
- release.yml: GitHub Actions workflow that validates, builds, creates DMG,
  publishes GitHub Release on CalVer tag push
- validate.yml: CI validation on push/PR for layout and script changes
- Info.plist now declares all 4 layouts (was only v2.0)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

EurKey-macOS.bundle/Contents/version.plist

@@ -3,10 +3,10 @@
 <plist version="1.0">
 <dict>
 	<key>BuildVersion</key>
-	<string></string>
+	<string>2026.03.03</string>
 	<key>ProjectName</key>
 	<string>EurKEY-macOS</string>
 	<key>SourceVersion</key>
-	<string></string>
+	<string>2026.03.03</string>
 </dict>
 </plist>