feat: explicit provider field replaces URL sniffing

LlmConfig.provider ("ollama" | "openai", empty = sniff URL so legacy
configs keep working). Settings presets set it — a custom-port Ollama
no longer falls into the OpenAI branch and fails confusingly.

Also: test_connection now accepts an optional config override — the
wizard was passing one that Rust silently ignored, so it tested the
saved config instead of the URL the user just typed.

src/components/FirstRunWizard.tsx

@@ -26,7 +26,7 @@ export function FirstRunWizard({ onComplete }: { onComplete: () => void }) {
       // Test connection to the default Ollama URL
       const result = await invoke<{ ok: boolean; models: string[]; error: string }>(
         "test_connection",
-        { config: { api_url: apiUrl, api_key: apiKey, model: "", temperature: 0.7, max_tokens: 512, top_p: 0.9, image_api_url: "", embed_model: "" } }
+        { config: { provider: "ollama", api_url: apiUrl, api_key: apiKey, model: "", temperature: 0.7, max_tokens: 512, top_p: 0.9, image_api_url: "", embed_model: "" } }
       );
       if (result.ok) {
         setModels(result.models);
@@ -52,6 +52,7 @@ export function FirstRunWizard({ onComplete }: { onComplete: () => void }) {
       // We'll just set the config and complete.
       await invoke("set_llm_config", {
         config: {
+          provider: "ollama",
           api_url: apiUrl,
           api_key: apiKey,
           model: model,

src/components/SettingsPanel.tsx

@@ -4,6 +4,8 @@ import { open } from "@tauri-apps/plugin-dialog";
 import { useToast } from "./Toast";
 
 interface LlmConfig {
+  /** "ollama" | "openai" — empty = let the backend sniff the URL. */
+  provider?: string;
   api_url: string;
   api_key: string;
   model: string;
@@ -174,16 +176,17 @@ export function SettingsPanel() {
     setImgTesting(false);
   }
 
-  // ponytail: provider presets fill in the API URL pattern + default model.
-  const PRESETS: { label: string; url: string; model: string; key?: boolean }[] = [
-    { label: "Ollama", url: "http://localhost:11434", model: "llama3.2" },
-    { label: "LM Studio", url: "http://localhost:1234/v1", model: "local-model" },
-    { label: "OpenAI", url: "https://api.openai.com", model: "gpt-4o-mini", key: true },
-    { label: "Custom", url: "", model: "" },
+  // ponytail: provider presets fill in the API URL pattern + default model
+  // + the API dialect (provider), so a custom-port Ollama isn't sniffed wrong.
+  const PRESETS: { label: string; url: string; model: string; provider: string; key?: boolean }[] = [
+    { label: "Ollama", url: "http://localhost:11434", model: "llama3.2", provider: "ollama" },
+    { label: "LM Studio", url: "http://localhost:1234/v1", model: "local-model", provider: "openai" },
+    { label: "OpenAI", url: "https://api.openai.com", model: "gpt-4o-mini", provider: "openai", key: true },
+    { label: "Custom", url: "", model: "", provider: "" },
   ];
-  function applyPreset(p: { url: string; model: string }) {
+  function applyPreset(p: { url: string; model: string; provider: string }) {
     if (!config) return;
-    setConfig({ ...config, api_url: p.url, model: p.model });
+    setConfig({ ...config, api_url: p.url, model: p.model, provider: p.provider });
     setConn(null);
   }
 
@@ -192,6 +195,7 @@ export function SettingsPanel() {
   // backend re-default on save — but we can't send a partial, so mirror the
   // known defaults here and toast.
   const DEFAULTS: LlmConfig = {
+    provider: "",
     api_url: "http://localhost:11434",
     api_key: "",
     model: "llama3.2",