Add PostgreSQL memory system for persistent user and conversation storage

- Add PostgreSQL database with SQLAlchemy async support
- Create models: User, UserFact, UserPreference, Conversation, Message, Guild, GuildMember
- Add custom name support so bot knows 'who is who'
- Add user facts system for remembering things about users
- Add persistent conversation history that survives restarts
- Add memory commands cog (!setname, !remember, !whatdoyouknow, !forgetme)
- Add admin commands (!setusername, !teachbot)
- Set up Alembic for database migrations
- Update docker-compose with PostgreSQL service
- Gracefully falls back to in-memory storage when DB not configured

docker-compose.yml

@@ -1,9 +1,32 @@
 services:
-  daemon-boyfriend:
-    build: .
-    container_name: daemon-boyfriend
-    restart: unless-stopped
-    env_file:
-      - .env
-    environment:
-      - PYTHONUNBUFFERED=1
+    daemon-boyfriend:
+        build: .
+        container_name: daemon-boyfriend
+        restart: unless-stopped
+        env_file:
+            - .env
+        environment:
+            - PYTHONUNBUFFERED=1
+            - DATABASE_URL=postgresql+asyncpg://daemon:${POSTGRES_PASSWORD:-daemon}@postgres:5432/daemon_boyfriend
+        depends_on:
+            postgres:
+                condition: service_healthy
+
+    postgres:
+        image: postgres:16-alpine
+        container_name: daemon-boyfriend-postgres
+        restart: unless-stopped
+        environment:
+            POSTGRES_USER: daemon
+            POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:-daemon}
+            POSTGRES_DB: daemon_boyfriend
+        volumes:
+            - postgres_data:/var/lib/postgresql/data
+        healthcheck:
+            test: ["CMD-SHELL", "pg_isready -U daemon -d daemon_boyfriend"]
+            interval: 10s
+            timeout: 5s
+            retries: 5
+
+volumes:
+    postgres_data: