feat(ai): Create unified AI package with OpenAI, Anthropic, and Gemini support

- Set up @mariozechner/ai package structure following monorepo patterns
- Install OpenAI, Anthropic, and Google Gemini SDK dependencies
- Document comprehensive API investigation for all three providers
- Design minimal unified API with streaming-first architecture
- Add models.dev integration for pricing and capabilities
- Implement automatic caching strategy for all providers
- Update project documentation with package creation guide

packages/ai/README.md

@@ -0,0 +1,62 @@
+# @mariozechner/ai
+
+Unified API for OpenAI, Anthropic, and Google Gemini LLM providers. This package provides a common interface for working with multiple LLM providers, handling their differences transparently while exposing a consistent, minimal API.
+
+## Features (Planned)
+
+- **Unified Interface**: Single API for OpenAI, Anthropic, and Google Gemini
+- **Streaming Support**: Real-time response streaming with delta events
+- **Tool Calling**: Consistent tool/function calling across providers
+- **Reasoning/Thinking**: Support for reasoning tokens where available
+- **Session Management**: Serializable conversation state across providers
+- **Token Tracking**: Unified token counting (input, output, cached, reasoning)
+- **Interrupt Handling**: Graceful cancellation of requests
+- **Provider Detection**: Automatic configuration based on endpoint
+- **Caching Support**: Provider-specific caching strategies
+
+## Installation
+
+```bash
+npm install @mariozechner/ai
+```
+
+## Quick Start (Coming Soon)
+
+```typescript
+import { createClient } from '@mariozechner/ai';
+
+// Automatically detects provider from configuration
+const client = createClient({
+  provider: 'openai',
+  apiKey: process.env.OPENAI_API_KEY,
+  model: 'gpt-4'
+});
+
+// Same API works for all providers
+const response = await client.complete({
+  messages: [
+    { role: 'user', content: 'Hello!' }
+  ],
+  stream: true
+});
+
+for await (const event of response) {
+  if (event.type === 'content') {
+    process.stdout.write(event.text);
+  }
+}
+```
+
+## Supported Providers
+
+- **OpenAI**: GPT-3.5, GPT-4, o1, o3 models
+- **Anthropic**: Claude models via native SDK
+- **Google Gemini**: Gemini models with thinking support
+
+## Development
+
+This package is part of the pi monorepo. See the main README for development instructions.
+
+## License
+
+MIT