feat(electron): bundle draw.io for offline support (#629)

* feat(electron): bundle draw.io for offline support

- Download draw.io static files during CI build (v29.3.5)
- Detect Electron and use local draw.io files instead of CDN
- Add offline=1 parameter to disable external service calls
- Skip /drawio path from i18n middleware redirect
- Add public/drawio/ to .gitignore (downloaded during build)

This allows the Electron app to work completely offline.

* chore: bump version to 0.4.12-beta.3 for offline test

* fix(electron): ad-hoc sign macOS app for bundled draw.io compatibility

* chore: bump version to 0.4.12-beta.4 for ad-hoc sign test

* fix(electron): disable electron-builder signing to use custom ad-hoc signing

* chore: bump version to 0.4.12-beta.5

package.json

@@ -1,6 +1,6 @@
 {
     "name": "next-ai-draw-io",
-    "version": "0.4.11",
+    "version": "0.4.12-beta.5",
     "license": "Apache-2.0",
     "private": true,
     "main": "dist-electron/main/index.js",