fix: latest.json must point to .tar.gz not .dmg for Tauri in-app updater

The Tauri updater plugin requires the .app.tar.gz artifact as the update
URL — not the .dmg installer. The DMG is for fresh installs only.
This was causing 'Install Update' to silently fail on all macOS builds
since the auto-updater infrastructure was set up.

Change ARM_DMG → ARM_TARBALL, pointing to the .app.tar.gz artifact.

.github/workflows/release.yml

@@ -176,7 +176,7 @@ jobs:
           REPO="refactoringhq/laputa-app"
 
           ARM_SIG=$(cat updater-aarch64/*.app.tar.gz.sig)
-          ARM_DMG=$(ls dmg-aarch64/*.dmg | xargs basename)
+          ARM_TARBALL=$(ls updater-aarch64/*.app.tar.gz | xargs basename)
 
           cat > latest.json << EOF
           {
@@ -186,7 +186,7 @@ jobs:
             "platforms": {
               "darwin-aarch64": {
                 "signature": "${ARM_SIG}",
-                "url": "https://github.com/${REPO}/releases/download/${TAG}/${ARM_DMG}"
+                "url": "https://github.com/${REPO}/releases/download/${TAG}/${ARM_TARBALL}"
               }
             }
           }