feat(electron): separate dev/uat build targets with isolated update channels

- Add build.dev.json to override publish.url for dev environment
- Add build:dev and build:uat scripts; each sets its own feed URL
- copy-to-nas.js now accepts env argument; outputs to
  electron-update/{dev|uat}/ locally and on NAS
- docker-compose volume mounts updated to serve from env subdirs
- Remove stale artifacts from electron-update root

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

electron/scripts/build.dev.json

@@ -0,0 +1,7 @@
+{
+  "publish": {
+    "provider": "generic",
+    "url": "http://192.168.1.14:7033/electron-update/",
+    "channel": "latest"
+  }
+}