Fix AdvancedPaste Gemini provider saving Azure placeholder endpoint (#44293)

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fix/what does it change/how was it tested (even manually, if necessary)?
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## Summary of the Pull Request
When creating/editing a Paste AI provider in Settings, providers that
don’t require an endpoint (e.g., Google/Gemini) could still end up
persisting the Azure OpenAI placeholder
(https://your-resource.openai.azure.com/) into settings.json.

### Fix:

- On save, for service types that don’t use an endpoint, prevent
placeholder/stale values from being persisted by forcing endpoint-url to
be empty.
- Reuse a single “requires endpoint” check so the dialog visibility and
save behavior stay consistent.

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## PR Checklist

- [x] Closes: #44243
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issues) -->
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
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- [ ] **Documentation updated:** If checked, please file a pull request
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and link it here: #xxx

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## Detailed Description of the Pull Request / Additional comments

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## Validation Steps Performed

## AI Generated Note:
This pull request refactors and improves how endpoint handling is
managed for different AI service types in the
`AdvancedPastePage.xaml.cs` file. The changes centralize the logic for
determining whether an endpoint is required, prevent persisting
placeholder or stale endpoint values for services that do not use them,
and ensure placeholder values are only provided where appropriate.

**Refactoring and logic centralization:**

* Introduced the `RequiresEndpointForService` helper method to
centralize and clarify the logic for determining if a service type
requires an endpoint, replacing inline checks in multiple places.
[[1]](diffhunk://#diff-14126907329c7fcd49dd33bab32283296c7dd68ddc3902163a482a3b3ce58d36L317-R317)
[[2]](diffhunk://#diff-14126907329c7fcd49dd33bab32283296c7dd68ddc3902163a482a3b3ce58d36R838-R845)

**Improved endpoint value handling:**

* Updated the dialog logic to ensure that endpoints are not persisted
for services that do not require them, preventing storage of placeholder
or irrelevant values.
* Modified the `GetEndpointPlaceholder` method to return an empty string
for service types that do not require an endpoint, rather than a generic
placeholder.

src/settings-ui/Settings.UI/SettingsXAML/Views/AdvancedPastePage.xaml.cs

@@ -314,10 +314,7 @@ namespace Microsoft.PowerToys.Settings.UI.Views
             string selectedType = draft.ServiceType ?? string.Empty;
             AIServiceType serviceKind = draft.ServiceTypeKind;
 
-            bool requiresEndpoint = serviceKind is AIServiceType.AzureOpenAI
-                or AIServiceType.AzureAIInference
-                or AIServiceType.Mistral
-                or AIServiceType.Ollama;
+            bool requiresEndpoint = RequiresEndpointForService(serviceKind);
             bool requiresDeployment = serviceKind == AIServiceType.AzureOpenAI;
             bool requiresApiVersion = serviceKind == AIServiceType.AzureOpenAI;
             bool requiresModelPath = serviceKind == AIServiceType.Onnx;
@@ -788,12 +785,17 @@ namespace Microsoft.PowerToys.Settings.UI.Views
             string serviceType = draft.ServiceType ?? "OpenAI";
             string apiKey = PasteAIApiKeyPasswordBox.Password;
             string trimmedApiKey = apiKey?.Trim() ?? string.Empty;
+            var serviceKind = draft.ServiceTypeKind;
+            bool requiresEndpoint = RequiresEndpointForService(serviceKind);
             string endpoint = (draft.EndpointUrl ?? string.Empty).Trim();
-            if (endpoint == string.Empty)
+
+            // Never persist placeholder text or stale values for services that don't use an endpoint.
+            if (!requiresEndpoint)
             {
-                endpoint = GetEndpointPlaceholder(draft.ServiceTypeKind);
+                endpoint = string.Empty;
             }
 
+            // For endpoint-based services, keep empty if the user didn't provide a value.
             if (RequiresApiKeyForService(serviceType) && string.IsNullOrWhiteSpace(trimmedApiKey))
             {
                 args.Cancel = true;
@@ -833,6 +835,14 @@ namespace Microsoft.PowerToys.Settings.UI.Views
             };
         }
 
+        private static bool RequiresEndpointForService(AIServiceType serviceKind)
+        {
+            return serviceKind is AIServiceType.AzureOpenAI
+                or AIServiceType.AzureAIInference
+                or AIServiceType.Mistral
+                or AIServiceType.Ollama;
+        }
+
         private static string GetEndpointPlaceholder(AIServiceType serviceKind)
         {
             return serviceKind switch
@@ -841,7 +851,7 @@ namespace Microsoft.PowerToys.Settings.UI.Views
                 AIServiceType.AzureAIInference => "https://{resource-name}.cognitiveservices.azure.com/",
                 AIServiceType.Mistral => "https://api.mistral.ai/v1/",
                 AIServiceType.Ollama => "http://localhost:11434/",
-                _ => "https://your-resource.openai.azure.com/",
+                _ => string.Empty,
             };
         }