Add Azure OpenAI Custom Model Integration (#1001)

Fixes #710 

This PR implements comprehensive Azure OpenAI integration for Dyad,
enabling users to leverage Azure
OpenAI models through proper environment variable configuration. The
implementation adds Azure as a
supported provider with full integration into the existing language
model architecture, including support
  for GPT-5 models. Key features include environment-based
configuration using `AZURE_API_KEY` and `AZURE_RESOURCE_NAME`,
specialized UI components that provide clear
setup instructions and status indicators, and seamless integration with
Dyad's existing provider system.
The Azure provider leverages the @ai-sdk/azure package (v1.3.25) for
compatibility with the current
  TypeScript language model interfaces.

The implementation includes robust error handling for missing
configuration, comprehensive test coverage
with 9 new unit tests covering critical functionality like model client
creation and error scenarios, and
  an E2E test for the Azure-specific settings UI. 

<img width="1510" height="908" alt="Screenshot 2025-08-18 at 9 14 32 PM"
src="https://github.com/user-attachments/assets/04aa99e1-1590-4bb0-86c9-a67b97bc7500"
/>

---------

Co-authored-by: graphite-app[bot] <96075541+graphite-app[bot]@users.noreply.github.com>
Co-authored-by: Will Chen <willchen90@gmail.com>

testing/fake-llm-server/index.ts

@@ -137,13 +137,20 @@ app.get("/lmstudio/api/v0/models", (req, res) => {
   res.json(lmStudioModels);
 });
 
-["lmstudio", "gateway", "engine", "ollama"].forEach((provider) => {
+["lmstudio", "gateway", "engine", "ollama", "azure"].forEach((provider) => {
   app.post(
     `/${provider}/v1/chat/completions`,
     createChatCompletionHandler(provider),
   );
 });
 
+// Azure-specific endpoints (Azure client uses different URL patterns)
+app.post("/azure/chat/completions", createChatCompletionHandler("azure"));
+app.post(
+  "/azure/openai/deployments/:deploymentId/chat/completions",
+  createChatCompletionHandler("azure"),
+);
+
 // Default test provider handler:
 app.post("/v1/chat/completions", createChatCompletionHandler("."));