feat: implement AI model API proxy service

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+zzrouter is an AI model API proxy service with OpenAI-compatible and Anthropic support, API key rotation, and request logging.
+
+## Project Structure
+
+```
+zzrouter/
+├── backend/     # Python FastAPI proxy server
+└── frontend/    # (placeholder)
+```
+
+## Backend Commands
+
+```bash
+cd backend
+
+# Install dependencies
+uv sync
+
+# Run development server
+uv run uvicorn app.main:app --reload --port 8000
+
+# Run directly
+uv run python main.py
+```
+
+## API Endpoints
+
+| Endpoint | Description |
+|----------|-------------|
+| `POST /v1/chat/completions` | OpenAI-compatible chat (auto-routes by model) |
+| `POST /v1/openai/chat/completions` | OpenAI native passthrough |
+| `POST /v1/anthropic/messages` | Anthropic native passthrough |
+| `GET /health` | Health check |
+
+## Authentication
+
+All API endpoints require Bearer token authentication:
+```
+Authorization: Bearer <client_key>
+```
+
+## Database
+
+SQLite database stored at `backend/data/zzrouter.db`.
+
+Key tables:
+- `client_keys` - Client API keys
+- `providers` - Model provider configs
+- `provider_keys` - Provider API keys (supports multiple per provider)
+- `request_logs` - Request statistics
+
+## Adding Configuration
+
+```sql
+-- Add a client key
+INSERT INTO client_keys (key, name) VALUES ('my-secret-key', 'my-app');
+
+-- Add provider API keys
+INSERT INTO provider_keys (provider_id, key) VALUES (1, 'sk-openai-key');
+INSERT INTO provider_keys (provider_id, key) VALUES (2, 'sk-ant-anthropic-key');
+```
+
+## Frontend
+
+Frontend directory is currently empty and pending implementation.