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

alembic/env.py

@@ -0,0 +1,86 @@
+"""Alembic migration environment configuration."""
+
+import asyncio
+from logging.config import fileConfig
+
+from sqlalchemy import pool
+from sqlalchemy.ext.asyncio import async_engine_from_config
+
+from alembic import context
+from daemon_boyfriend.config import settings
+from daemon_boyfriend.models import Base
+
+# this is the Alembic Config object
+config = context.config
+
+# Interpret the config file for Python logging
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+# Model metadata for autogenerate support
+target_metadata = Base.metadata
+
+
+def get_url() -> str:
+    """Get database URL from settings."""
+    url = settings.database_url
+    if not url:
+        raise ValueError("DATABASE_URL must be set for migrations")
+    return url
+
+
+def run_migrations_offline() -> None:
+    """Run migrations in 'offline' mode.
+
+    This configures the context with just a URL and not an Engine,
+    though an Engine is acceptable here as well. By skipping the Engine creation
+    we don't even need a DBAPI to be available.
+
+    Calls to context.execute() here emit the given string to the script output.
+    """
+    url = get_url()
+    context.configure(
+        url=url,
+        target_metadata=target_metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+    )
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def do_run_migrations(connection) -> None:
+    """Run migrations with the given connection."""
+    context.configure(connection=connection, target_metadata=target_metadata)
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+async def run_async_migrations() -> None:
+    """Run migrations in async mode."""
+    configuration = config.get_section(config.config_ini_section, {})
+    configuration["sqlalchemy.url"] = get_url()
+
+    connectable = async_engine_from_config(
+        configuration,
+        prefix="sqlalchemy.",
+        poolclass=pool.NullPool,
+    )
+
+    async with connectable.connect() as connection:
+        await connection.run_sync(do_run_migrations)
+
+    await connectable.dispose()
+
+
+def run_migrations_online() -> None:
+    """Run migrations in 'online' mode."""
+    asyncio.run(run_async_migrations())
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()