add build workflow, remove redundant validate workflow

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

.github/workflows/build.yml

@@ -0,0 +1,36 @@
+name: Build
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'EurKey-macOS.bundle/**'
+      - 'scripts/**'
+      - 'spec/**'
+  pull_request:
+    paths:
+      - 'EurKey-macOS.bundle/**'
+      - 'scripts/**'
+      - 'spec/**'
+
+jobs:
+  build:
+    runs-on: macos-latest
+    steps:
+      - name: checkout
+        uses: actions/checkout@v4
+
+      - name: validate layouts
+        run: python3 scripts/validate_layouts.py
+
+      - name: build bundle
+        run: bash scripts/build-bundle.sh
+
+      - name: create DMG
+        run: bash scripts/create-dmg.sh
+
+      - name: upload DMG
+        uses: actions/upload-artifact@v4
+        with:
+          name: EurKEY-macOS-DMG
+          path: build/*.dmg