V1.12.3: live updates behind any proxy, fewer requests

- Live updates start on plain requests and move up to a websocket when
  one gets through. The site used to ask for the websocket first, with
  no way back: behind a proxy that does not pass the upgrade, nothing
  live arrived at all.
- A browser asks the API's leave before a request, the site and the API
  being on different hosts. It now remembers the answer for two hours,
  where it used to ask before nearly every request.
- A built file is kept by the browser for good: its name changes when
  its contents do. Each used to be checked again on every page load.
- For a real websocket through nginx, the blocks that pass requests to
  the API need "proxy_http_version 1.1", "proxy_set_header Upgrade
  $http_upgrade" and "proxy_set_header Connection "upgrade"".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

package-lock.json

@@ -1,19 +1,19 @@
 {
   "name": "dnd-campaign-manager",
-  "version": "1.12.2",
+  "version": "1.12.3",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "dnd-campaign-manager",
-      "version": "1.12.2",
+      "version": "1.12.3",
       "workspaces": [
         "backend",
         "frontend"
       ]
     },
     "backend": {
-      "version": "1.12.2",
+      "version": "1.12.3",
       "dependencies": {
         "@prisma/adapter-pg": "^7.10.0",
         "@prisma/client": "^7.10.0",
@@ -33,7 +33,7 @@
       }
     },
     "frontend": {
-      "version": "1.12.2",
+      "version": "1.12.3",
       "dependencies": {
         "@tanstack/react-query": "^5.103.2",
         "axios": "^1.20.0",