Add README documentation

Documents service purpose, endpoints, database schema, and configuration.

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

README.md

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+# Recall Service
+
+Memory and data persistence for Egregore.
+
+## Purpose
+
+Stores and retrieves conversation messages using PostgreSQL. Provides the persistent memory that allows conversations to continue across sessions.
+
+## Endpoints
+
+| Endpoint | Method | Description |
+|----------|--------|-------------|
+| `/messages` | POST | Save a single message |
+| `/messages` | GET | Get messages with pagination |
+| `/messages/blocks` | POST | Save multiple response blocks |
+| `/messages/history` | GET | Get history in Claude API format |
+| `/messages/search` | GET | Full-text search messages |
+| `/health` | GET | Health check |
+
+## Configuration
+
+Environment variables (from `~/.env`):
+
+| Variable | Description | Default |
+|----------|-------------|---------|
+| `DATABASE_URL` | PostgreSQL connection string | `postgresql://egregore:...@localhost/egregore` |
+
+## Running
+
+```bash
+# Activate venv
+source ~/.venv/bin/activate
+
+# Run directly
+python main.py
+
+# Or via systemd
+sudo systemctl start recall
+sudo systemctl status recall
+```
+
+## Database Schema
+
+Messages table with:
+- `id` - Auto-increment primary key
+- `role` - user/assistant
+- `type` - text/tool_use/tool_result
+- `content` - Message content
+- `group_id` - Groups related messages
+- `metadata` - JSON for tool info
+- `priority` - For notification decisions
+- `timestamp` - When saved
+
+Includes full-text search index on content.
+
+## Dependencies
+
+- FastAPI
+- asyncpg (PostgreSQL async driver)