hotfix(build): npm run dist 가 Mac arm64 에서도 동작하도록 cross-platform

- dist / dist:dir 에서 --win --x64 제거 → electron-builder host-default
  (Windows 에선 win-x64, Mac 에선 mac-arm64 자동 선택)
- 명시적 강제 variant 추가: dist:win, dist:mac
- build.mac 블록 추가:
  - target: dmg / arch: arm64
  - category: productivity
  - identity: null (개인 dogfood, codesign skip)

검증:
- typecheck 0
- 단위 403/403
- npm run dist:dir on Windows: platform=win32 arch=x64 (회귀 X)

Mac arm64 빌드 시 첫 실행 시 "Apple 이 검증할 수 없음" 경고 → 우클릭 → 열기 (codesign 미적용 의도).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -22,9 +22,13 @@
     "test:e2e": "playwright test",
     "typecheck": "tsc --noEmit",
     "predist": "npm run rebuild:electron && npm run build",
-    "dist": "electron-builder --win --x64",
+    "dist": "electron-builder",
     "predist:dir": "npm run rebuild:electron && npm run build",
-    "dist:dir": "electron-builder --dir --win --x64"
+    "dist:dir": "electron-builder --dir",
+    "predist:win": "npm run rebuild:electron && npm run build",
+    "dist:win": "electron-builder --win --x64",
+    "predist:mac": "npm run rebuild:electron && npm run build",
+    "dist:mac": "electron-builder --mac --arm64"
   },
   "build": {
     "appId": "xyz.altair823.inkling",
@@ -47,6 +51,13 @@
       "allowToChangeInstallationDirectory": true,
       "deleteAppDataOnUninstall": false,
       "shortcutName": "Inkling"
+    },
+    "mac": {
+      "target": [
+        { "target": "dmg", "arch": ["arm64"] }
+      ],
+      "category": "public.app-category.productivity",
+      "identity": null
     }
   },
   "dependencies": {