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>

.github/workflows/release.yml

@@ -0,0 +1,51 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - '[0-9][0-9][0-9][0-9].[0-9][0-9].[0-9][0-9]*'
+
+permissions:
+  contents: write
+
+jobs:
+  release:
+    runs-on: macos-latest
+    steps:
+      - name: checkout
+        uses: actions/checkout@v4
+
+      - name: extract version from tag
+        id: version
+        run: echo "version=${GITHUB_REF_NAME}" >> "$GITHUB_OUTPUT"
+
+      - name: validate layouts
+        run: python3 scripts/validate_layouts.py
+
+      - name: build bundle
+        run: bash scripts/build-bundle.sh --version "${{ steps.version.outputs.version }}"
+
+      - name: create DMG
+        run: bash scripts/create-dmg.sh --version "${{ steps.version.outputs.version }}"
+
+      - name: create GitHub release
+        uses: softprops/action-gh-release@v2
+        with:
+          name: EurKEY-macOS ${{ steps.version.outputs.version }}
+          files: build/EurKEY-macOS-${{ steps.version.outputs.version }}.dmg
+          body: |
+            ## Installation
+
+            1. Download `EurKEY-macOS-${{ steps.version.outputs.version }}.dmg`
+            2. Open the DMG
+            3. Drag `EurKey-macOS.bundle` to the `Install Here (Keyboard Layouts)` folder
+            4. Log out and back in (or restart)
+            5. System Settings → Keyboard → Input Sources → Add → Select EurKEY
+
+            ## Included layouts
+
+            - **EurKEY v1.2** — legacy version
+            - **EurKEY v1.3** — official spec implementation
+            - **EurKEY v1.4** — v1.3 with ẞ on Caps+§
+            - **EurKEY v2.0** — custom edition
+          generate_release_notes: true