Add README documentation

Documents service purpose, endpoints, rate limiting, tool system, and configuration.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

README.md

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+# Reason Service
+
+AI reasoning and LLM integration for Egregore.
+
+## Purpose
+
+Processes conversations with Claude, handles tool execution, and manages the AI reasoning loop. This is where the "thinking" happens.
+
+## Endpoints
+
+| Endpoint | Method | Description |
+|----------|--------|-------------|
+| `/process` | POST | Process conversation with tool loop |
+| `/tool` | POST | Execute a single tool directly |
+| `/tools` | GET | List available tool definitions |
+| `/prompt` | GET | Get current system prompt |
+| `/health` | GET | Health check |
+
+## Configuration
+
+Environment variables (from `~/.env`):
+
+| Variable | Description | Default |
+|----------|-------------|---------|
+| `ANTHROPIC_API_KEY` | Claude API key | Required |
+| `RATE_LIMIT` | Requests per minute | `10/minute` |
+
+## Running
+
+```bash
+# Activate venv
+source ~/.venv/bin/activate
+
+# Run directly
+python main.py
+
+# Or via systemd
+sudo systemctl start reason
+sudo systemctl status reason
+```
+
+## Rate Limiting
+
+Built-in rate limiting (10 req/min per IP) protects against API abuse. Configure via `RATE_LIMIT` env var.
+
+## Tool System
+
+The service supports a tool loop pattern:
+1. Receive conversation history
+2. Call Claude API
+3. If Claude requests tool use, execute tools
+4. Feed results back to Claude
+5. Repeat until Claude produces final response
+
+Tools are defined in `tools.py` and include system operations available to the AI.
+
+## Dependencies
+
+- FastAPI
+- anthropic (Claude API client)
+- slowapi (rate limiting)