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

.github/copilot-instructions.md

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+# 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` |