fix(server): count quota by the key actually used, and more review fixes

Found by the PR review, each with a test that failed first:
- Quota: any key header skipped it, even one the provider never reads
  (x-aws-access-key-id with OpenAI), so a request ran on the server's
  key without being counted. The check now runs after the model is
  resolved and uses usesServerCredentials. On main already.
- usesServerCredentials read the raw base URL; "/" cleans up to none, so
  an Ollama request ran on the server's key past the server-model check.
- SGLang's default 127.0.0.1:8000 only fills the settings form. Chat and
  the model list used it as a real address, so the server called its own
  machine even with private URLs blocked. Now a base URL is required.
- With a user's OpenAI key and no base URL, the SDK read the server's
  OPENAI_BASE_URL. The official endpoint is now passed. On main already.
- The Test button refused nothing on the server's keys (Ollama Cloud),
  and a 15 s timeout reported "connected, no tool call".
- The model list for Ollama without a base URL came from ollama.com while
  chat went to the server's Ollama.
- Bedrock's "Too many tokens, please wait" counted as context too long.
- On the server's keys the provider's error text stays in the server log;
  it can name the server's AWS account, role or internal hosts.
- Desktop app: the preset keys are the user's own (NEXT_AI_DRAWIO_DESKTOP),
  so Max Output Tokens can be raised and keyless models in settings work
  again. A launch that found the remembered port taken no longer replaces
  it, which hid the user's chats and settings for good.

tests/unit/validate-model-route.test.ts

@@ -74,6 +74,50 @@ describe("POST /api/validate-model", () => {
         expect(typeof data.responseTime).toBe("number")
     })
 
+    it("reports a model that did not answer in time", async () => {
+        // The 15 s timeout has fired: the SDK ends the stream with an
+        // abort part instead of throwing
+        const timedOut = AbortSignal.abort(
+            new DOMException("The operation timed out.", "TimeoutError"),
+        )
+        const timeout = vi
+            .spyOn(AbortSignal, "timeout")
+            .mockReturnValue(timedOut)
+        vi.stubGlobal(
+            "fetch",
+            vi.fn(async () => {
+                throw timedOut.reason
+            }),
+        )
+        try {
+            const data = await testGlm()
+            expect(data.valid).toBe(false)
+            expect(data.code).toBe("timeout")
+        } finally {
+            timeout.mockRestore()
+        }
+    })
+
+    it("does not run on the server's keys", async () => {
+        process.env.OLLAMA_API_KEY = "server-ollama-key"
+        try {
+            const res = await validateModel(
+                new Request("http://localhost/api/validate-model", {
+                    method: "POST",
+                    headers: { "Content-Type": "application/json" },
+                    body: JSON.stringify({
+                        provider: "ollama",
+                        modelId: "any-cloud-model",
+                    }),
+                }),
+            )
+            expect(res.status).toBe(400)
+            expect((await res.json()).error).toMatch(/API key/)
+        } finally {
+            delete process.env.OLLAMA_API_KEY
+        }
+    })
+
     it("warns when the model answers without a tool call", async () => {
         streamReply({ role: "assistant", content: "OK" })
         const data = await testGlm()