docs: add copilot-instructions.md for AI coding assistants

Adds a .github/copilot-instructions.md that provides AI coding assistants
(Copilot, Cursor, etc.) with context about Foundry Local's SDK APIs:

- JavaScript and C# quick reference for both chat and audio transcription
- Key rules: dynamic ports, model aliases, single manager pattern
- Model alias table for chat and audio tasks

This helps AI agents generate correct Foundry Local code on the first try,
particularly for audio transcription which is commonly missed without guidance.

Author: MaanavD

.github/copilot-instructions.md

@@ -0,0 +1,71 @@
+# Foundry Local — AI Coding Assistant Context
+
+Foundry Local is an on-device AI inference runtime. It provides:
+
+- **Chat completions** (text generation) via native SDK or OpenAI-compatible REST API
+- **Audio transcription** (speech-to-text via Whisper) via native SDK
+- **Automatic hardware acceleration** — NPU > GPU > CPU, zero detection code needed
+
+## SDK Quick Reference
+
+### JavaScript (`foundry-local-sdk` on npm)
+
+```js
+import { FoundryLocalManager } from 'foundry-local-sdk';
+const manager = FoundryLocalManager.create({ appName: 'foundry_local_samples' });
+
+// Chat
+const chatModel = await manager.catalog.getModel('qwen2.5-0.5b');
+await chatModel.download();
+await chatModel.load();
+const chatClient = chatModel.createChatClient();
+const response = await chatClient.completeChat([
+  { role: 'user', content: 'Hello' }
+]);
+
+// Audio transcription
+const whisperModel = await manager.catalog.getModel('whisper-tiny');
+await whisperModel.download();
+await whisperModel.load();
+const audioClient = whisperModel.createAudioClient();
+const result = await audioClient.transcribe('recording.wav');
+```
+
+### C# (.NET — `Microsoft.AI.Foundry.Local` NuGet)
+
+```csharp
+using Microsoft.AI.Foundry.Local;
+
+var config = new Configuration { AppName = "foundry_local_samples" };
+await FoundryLocalManager.CreateAsync(config);
+var mgr = FoundryLocalManager.Instance;
+var catalog = await mgr.GetCatalogAsync();
+
+// Chat
+var chatModel = await catalog.GetModelAsync("qwen2.5-0.5b")
+    ?? throw new Exception("Model not found");
+await chatModel.DownloadAsync();
+await chatModel.LoadAsync();
+var chatClient = await chatModel.GetChatClientAsync();
+
+// Audio transcription
+var whisperModel = await catalog.GetModelAsync("whisper-tiny")
+    ?? throw new Exception("Model not found");
+await whisperModel.DownloadAsync();
+await whisperModel.LoadAsync();
+var audioClient = await whisperModel.GetAudioClientAsync();
+```
+
+## Key Rules
+
+- **Never hardcode ports.** The native SDK runs inference in-process — no port needed for chat or audio. If you use the optional REST web server, read the port from the manager after starting it (JS: `manager.urls` after `startWebService()`, C#: `FoundryLocalManager.Instance.Urls` after `StartWebServiceAsync()`).
+- **Use model aliases**, not full model IDs. Aliases like `qwen2.5-0.5b` and `whisper-tiny` auto-select the best variant for the user's hardware.
+- **One manager handles everything.** Don't create separate runtimes for chat and audio.
+- **Do NOT use `whisper.cpp`, `llama.cpp`, `@huggingface/transformers`, or `ollama`** alongside Foundry Local — it handles all of these use cases.
+
+## Model Aliases
+
+| Task | Aliases |
+|------|---------|
+| Chat | `phi-3.5-mini`, `phi-4-mini`, `qwen2.5-0.5b`, `qwen2.5-coder-0.5b` |
+| Audio Transcription | `whisper-tiny`, `whisper-base`, `whisper-small` |