Add custom API URL and model to AI settings

- Settings → AI: optional base URL and model name fields
- Defaults to Anthropic/OpenAI public APIs when left blank
- Custom URL enables Open WebUI, LM Studio, Ollama, and any OpenAI-compatible endpoint
- Parse endpoint uses custom base URL and model if configured
- Migration 0004: ai_base_url + ai_model columns on users
- OpenAI provider label updated to "OpenAI-compatible"

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/settings/SettingsPage.tsx

@@ -658,6 +658,8 @@ function AiSection() {
   const qc = useQueryClient();
   const [provider, setProvider] = useState("anthropic");
   const [apiKey, setApiKey]     = useState("");
+  const [baseUrl, setBaseUrl]   = useState("");
+  const [model, setModel]       = useState("");
   const [showKey, setShowKey]   = useState(false);
   const [success, setSuccess]   = useState("");
 
@@ -666,16 +668,23 @@ function AiSection() {
     queryFn: async () => {
       const d = await getAiSettings();
       if (d.provider) setProvider(d.provider);
+      if (d.base_url) setBaseUrl(d.base_url);
+      if (d.model) setModel(d.model);
       return d;
     },
   });
 
   const saveMutation = useMutation({
-    mutationFn: () => saveAiSettings(provider, apiKey),
+    mutationFn: () => saveAiSettings({
+      provider,
+      api_key: apiKey,
+      base_url: baseUrl,
+      model,
+    }),
     onSuccess: () => {
       qc.invalidateQueries({ queryKey: ["ai-settings"] });
       setApiKey("");
-      setSuccess("API key saved");
+      setSuccess("Settings saved");
       setTimeout(() => setSuccess(""), 3000);
     },
   });
@@ -684,11 +693,15 @@ function AiSection() {
     mutationFn: clearAiSettings,
     onSuccess: () => {
       qc.invalidateQueries({ queryKey: ["ai-settings"] });
-      setSuccess("API key removed");
+      setBaseUrl(""); setModel("");
+      setSuccess("AI settings removed");
       setTimeout(() => setSuccess(""), 3000);
     },
   });
 
+  const defaultModel = provider === "anthropic" ? "claude-haiku-4-5-20251001" : "gpt-4o-mini";
+  const defaultUrl   = provider === "anthropic" ? "https://api.anthropic.com" : "https://api.openai.com";
+
   return (
     <div className={cardCls}>
       <div className="flex items-center gap-2">
@@ -723,8 +736,11 @@ function AiSection() {
           className={inputCls}
         >
           <option value="anthropic">Anthropic (Claude)</option>
-          <option value="openai">OpenAI (GPT-4o mini)</option>
+          <option value="openai">OpenAI-compatible</option>
         </select>
+        <p className="text-xs text-muted-foreground mt-1">
+          OpenAI-compatible works with Open WebUI, LM Studio, Ollama, and any OpenAI-spec endpoint.
+        </p>
       </div>
 
       <div>
@@ -737,7 +753,7 @@ function AiSection() {
             value={apiKey}
             onChange={e => setApiKey(e.target.value)}
             className={cn(inputCls, "pr-10")}
-            placeholder={current?.has_api_key ? "••••••••••••••••" : provider === "anthropic" ? "sk-ant-..." : "sk-..."}
+            placeholder={current?.has_api_key ? "••••••••••••••••" : provider === "anthropic" ? "sk-ant-..." : "sk-... (use any value if not required)"}
           />
           <button
             type="button"
@@ -747,10 +763,33 @@ function AiSection() {
             {showKey ? <EyeOff className="w-4 h-4" /> : <Eye className="w-4 h-4" />}
           </button>
         </div>
+      </div>
+
+      <div>
+        <label className="text-sm font-medium block mb-1.5">Custom API URL <span className="text-muted-foreground font-normal">(optional)</span></label>
+        <input
+          type="text"
+          value={baseUrl}
+          onChange={e => setBaseUrl(e.target.value)}
+          className={inputCls}
+          placeholder={defaultUrl}
+        />
         <p className="text-xs text-muted-foreground mt-1">
-          {provider === "anthropic"
-            ? "Get your key at console.anthropic.com → API Keys"
-            : "Get your key at platform.openai.com → API Keys"}
+          Leave blank to use the default. For Open WebUI: <code className="bg-secondary px-1 rounded">http://your-server:3000</code>
+        </p>
+      </div>
+
+      <div>
+        <label className="text-sm font-medium block mb-1.5">Model <span className="text-muted-foreground font-normal">(optional)</span></label>
+        <input
+          type="text"
+          value={model}
+          onChange={e => setModel(e.target.value)}
+          className={inputCls}
+          placeholder={defaultModel}
+        />
+        <p className="text-xs text-muted-foreground mt-1">
+          Leave blank to use the default. For Open WebUI, enter the model name exactly as shown in its interface.
         </p>
       </div>
 
@@ -761,7 +800,7 @@ function AiSection() {
           className="flex items-center gap-2 bg-primary text-primary-foreground px-4 py-2 rounded-lg text-sm font-medium hover:bg-primary/90 disabled:opacity-50 transition-colors"
         >
           {saveMutation.isPending && <Loader2 className="w-4 h-4 animate-spin" />}
-          {current?.has_api_key && !apiKey ? "Update provider" : "Save API key"}
+          Save settings
         </button>
 
         {current?.has_api_key && (