feat(build): aggiunge infrastruttura Docker per build Linux riproducibile

- contrib/linux: Dockerfile (node:20-bookworm-slim) e build.sh con mount CA certs
- package.json: target linux (AppImage/deb), files whitelist, electron in devDependencies
- main.js: icona finestra impostata esplicitamente per Linux
- build/.gitkeep: cartella build tracciata per icon.ico e icon.png

package.json

@@ -14,16 +14,29 @@
   "build": {
     "appId": "com.cadroute",
     "productName": "CadRoute",
+    "files": [
+      "main.js",
+      "preload.js",
+      "renderer/**/*",
+      "services/**/*",
+      "build/icon.png"
+    ],
     "win": {
-      "target": "nsis"
+      "target": "nsis",
+      "icon": "build/icon.ico"
+    },
+    "linux": {
+      "target": ["AppImage", "deb"],
+      "icon": "build/icon.png",
+      "category": "Utility"
     }
   },
   "dependencies": {
-    "electron": "^40.7.0",
     "fs-extra": "^11.3.4",
     "unzipper": "^0.12.3"
   },
   "devDependencies": {
+    "electron": "^40.7.0",
     "electron-builder": "^26.8.1"
   }
 }