Fix image upload: use Tauri HTTP plugin to bypass WebView fetch restrictions

src-tauri/capabilities/default.json

@@ -7,6 +7,12 @@
     "core:default",
     "opener:default",
     "updater:default",
-    "process:default"
+    "process:default",
+    {
+      "identifier": "http:default",
+      "allow": [
+        { "url": "https://nostr.build/**" }
+      ]
+    }
   ]
 }