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/provider-models.test.ts

@@ -103,6 +103,29 @@ describe("listProviderModels", () => {
         ])
     })
 
+    it("lists Ollama from where chat goes without a base URL", async () => {
+        const { fn, calls } = answer({ models: [{ name: "llama3.2" }] })
+        process.env.OLLAMA_BASE_URL = "http://ollama.internal:11434"
+        try {
+            await listProviderModels("ollama", {}, fn)
+        } finally {
+            delete process.env.OLLAMA_BASE_URL
+        }
+        await listProviderModels("ollama", {}, fn)
+        expect(calls.map((c) => c.url)).toEqual([
+            "http://ollama.internal:11434/api/tags",
+            "http://127.0.0.1:11434/api/tags",
+        ])
+    })
+
+    it("does not use SGLang's local address as a default", async () => {
+        const { fn, calls } = answer({ data: [] })
+        await expect(
+            listProviderModels("sglang", { apiKey: "k" }, fn),
+        ).rejects.toThrow(/base URL/)
+        expect(calls).toHaveLength(0)
+    })
+
     it("turns a failed request into an error with its status", async () => {
         const { fn } = answer({ error: "bad key" }, 401)
         await expect(