fix(server): use the keys the user sent, and more review fixes

Found by the second PR review:
- With AWS_BEARER_TOKEN_BEDROCK set on the server, a request with the
  user's AWS keys ran on the server's token: the Bedrock SDK prefers it.
  Checked with Bedrock: invalid user keys used to get an answer.
- An OpenAI key with the official URL filled in (the settings form does
  that) went to the Responses API. Back to main's rule: a configured base
  URL uses Chat Completions.
- A user's Ollama key went to the server's OLLAMA_BASE_URL, for chat and
  for the model list. Like every other provider, it goes to the user's
  base URL or Ollama Cloud.
- The server's keyless Ollama and EdgeOne were not counted in the quota.
- AI_MODEL models on the server's keys ran on any provider with a server
  key, not only on AI_PROVIDER.
- A user's Azure key without a base URL used the server's resource name.
- The admin panel's Test button failed whenever access codes were set.
- DeepSeek's errors in the stream (plain text) were shown as they were,
  without a hint and also on the server's keys. Bedrock's throttling in
  the stream was not recognised as a rate limit.
- The EdgeOne function accepted text/plain; x=application/json, which
  other sites can send without a CORS preflight.
- Desktop app: a launch that found the old port taken for a moment (the
  previous version still quitting after an update) remembered the new
  port for good. The new port is kept only when Windows reserves the old
  one. A failed read of the presets file moved it aside as corrupt, and a
  save could then replace the presets. Switching presets on the same port
  now reloads the page. The dev launcher no longer misses a preset change
  made before or during a restart.

edge-functions/api/edgeai/chat/completions.ts

@@ -97,11 +97,13 @@ function hasValidAccessCode(request: Request, env: any): boolean {
 
 export async function onRequest({ request, env }: any) {
     // Requiring JSON also makes any cross-site browser request need a CORS
-    // preflight, which fails without CORS headers
-    if (
-        request.method !== "POST" ||
-        !request.headers.get("content-type")?.includes("application/json")
-    ) {
+    // preflight, which fails without CORS headers. Only the type before any
+    // parameters counts: "text/plain; x=application/json" needs none.
+    const mediaType = (request.headers.get("content-type") ?? "")
+        .split(";")[0]
+        .trim()
+        .toLowerCase()
+    if (request.method !== "POST" || mediaType !== "application/json") {
         return createResponse(
             {
                 error: {