fix(updater): show header action only when update is available

Hide the header update action until a newer release is confirmed.
Register update notifications before renderer initialization so startup cannot miss them.
Refresh the public product screenshot and release metadata for v2.0.7.

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "multi-hoster-uploader",
-  "version": "2.0.6",
+  "version": "2.0.7",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "multi-hoster-uploader",
-      "version": "2.0.6",
+      "version": "2.0.7",
       "dependencies": {
         "chokidar": "^3.6.0",
         "undici": "^7.29.0",